1 Introduction

Donald J. Trump’s presidency was unorthodox in many respects. Foreign and security policies can certainly be considered as one such notable example. His “America First” platform, while often viewed as populist politics, entailed concrete policy positions, not least ones that diverged from the traditional role of the United States in the international arena. A core strategy of Trump’s foreign policy was, for example, the withdrawal from international organizations and international commitments, ranging from climate policy agreements to arms control treaties. These decisions thus had a transformative impact on international politics, with severe repercussions for traditional U.S. allies in Europe and Asia (see Herr and Müller 2019), making this facet of “Trumpism” a relevant case of analysis within the scope of this special issue. While numerous studies have focused on the Trump administration’s foreign and security policies (see, e.g., Löfflmann 2019; Cooley and Nexon 2020; Olsen 2021), this article considers the domestic support and contestation toward President Trump’s international policies in Congress, and here in particular the role of the Republican Party (GOP).

Given Trump’s predominant influence over the Republican Party, in particular his loyal base (see Blum and Parker 2019), one could have expected little resistance to the administration’s “swinging the wrecking ball” toward the traditional pillars of U.S. foreign policy. Indeed, GOP members in the House of Representatives and the Senate overall supported Trump in 92% and 87% of all roll call votes, respectively.Footnote 1 And yet, some of Trump’s most prominent defeats in Congress concerned international issues: For example, the strengthening of sanctions against Russia in July 2017 (H.R. 3364), and Congress’s only successful veto override against Trump on the defense budget in December 2020 (H.R. 6395). At the same time, GOP members of Congress (MoC) regularly applauded Trump’s “America First” policy. Tom Cotton (R-AR), for example, a staunch supporter of the president’s policies, described the “America First” doctrine as “healthy nationalism” (cited in Beauchamp 2017). In a similar vein, Representative Mark Meadows (R-NC) hailed Trump’s decision to end the Iran nuclear deal as a “victory for a safer and more secure America” (cited in Homan and Lantis 2020, p. 151).

What explains this variance in defiance and acquiescence among GOP members in Congress? This pattern is puzzling not only in view of Trump’s dominance of the GOP on many domestic policy issues, but also in regard to post–Cold War foreign policy. For example, the Republican Party remained typically loyal to their president, George W. Bush, even after public criticism rose against the war in Iraq (Goble and Holm 2009, p. 226). Furthermore, if bipartisanship in foreign policy is generally in decline and “hyperpartisanship” is the new norm (Trubowitz and Harris 2019, p. 619; see Schultz 2017), we would expect support for the president on international issues to follow partisan patterns.

To address this puzzle, I will first trace the extent and contours of polarization in Congress on foreign policy, with a particular focus on the Obama and Trump presidencies, to systematically assess the degree of support and opposition in a comparative perspective. The analysis underscores that the reaction to Trump’s “America First” policy was not uniform. To further reveal the sources of the variance, the paper then presents a comparative case study on two policy areas with mixed GOP positioning: foreign aid (contra Trump) and arms control (pro Trump). The analysis also considers to what extent Republicans in Congress continued or shifted their position from Obama to Trump. In sum, the article indicates that traditionalists among Republicans opposed some of Trump’s anti-internationalist policies, in particular those that contradicted established GOP ideological positions regarding vital U.S. security interests. At the same time, Republicans supported Trump on issues where the GOP could continue its policy preference (in particular, arms control).

Understanding GOP positioning toward Trump on international issues is not only relevant in order to fully grasp the partisan dynamics within the Republican Party, but is also significant in view of the impact of the domestic politics of U.S. foreign policy on international relations. Congressional assertiveness against Trump may have, for example, reassured European allies that the nationalist “America First” agenda would not be fully implemented. Connectedly, contestation against Trump’s foreign policy, including from within the Republican Party, signaled international partners—but arguably adversaries, too—that the Trump administration’s policies might by reversed in the case of a new president. Seen from this perspective, the article contributes to this special issue’s aim to understand the “complexly contested” U.S. policies and politics.

2 Polarization Beyond the Water’s Edge: State of the Art and Research Propositions

Although it is well established that partisan polarization did not start with Donald Trump (Berg 2021, p. 38), his divisive campaign and unorthodox presidency are commonly described as an additional catalyst for societal and elite polarization (see Sirakov 2020; Harnisch and Friedrichs 2021). While polarization on domestic issues, such as economic and social issues, abortion rights, gun control, and environmental policies, has led to entrenched positions and gridlock in Washington, D.C., as well as to polarization between the federal government and the states (e.g., Jacobsen 2013; Sonnicksen 2022), the extent of polarization on international issues has been subject to scholarly debate. Conventional wisdom in the United States has long been that politics “stops at the water’s edge” (see Lewis 2017). In other words, foreign and security policy issues are exempt from the typical partisan infighting that structures domestic politics, also because there had been a rather broad internationalist consensus among major parties regarding the U.S. role as a liberal hegemon (Trubowitz and Harris 2019). Foreign policy scholars have diagnosed cracks in this overarching consensus since the war in Vietnam, when Congress and the president fought over budget and strategy of the intervention, while voters took to the street to protest the war (McCormick and Wittkopf 1990).Footnote 2 With the end of the Cold War, another important source for the remaining stability of the consensus on international issues disappeared (DeLaet and Scott 2006). Against this backdrop, Kupchan and Trubowitz (2007) have argued that foreign policy bipartisanship has declined since the 1970s and that the terrorist attacks of 9/11 failed to produce a new consensus.

Kupchan and Trubowitz’s provocative thesis of a “dead center” (2007) on international issues in Congress has received criticism. Chaudion et al. (2010), for example, offer an alternative argument focusing on substantive legislation (instead of all roll call votes) and contend that the “center still holds.” Despite the extensive body of research that this controversy produced (see Hurst and Wroe 2016; Trubowitz and Mellow 2011), there is still no consensus among scholars on whether polarization on foreign and security policy is continuously on the rise to an extent more or less akin to the development on domestic issues (see Friedrichs and Tama 2022 for a recent overview). Several findings can be distilled from this research nonetheless: First, polarization on international issues is relatively lower compared to that on domestic issues, and there is still more bipartisanship on foreign and security policy than on domestic topics (Bryan and Tama 2021, p. 15; Wagner 2020, p. 49). Second, there is substantial variance within the issue area of international politics. In some areas, foreign policy decisions during the post–Cold War era have become highly politicized, unlike before 1991. This includes issues such as arms control (Kreps et al. 2018), human rights (Homan and Lantis 2020), and military interventions (Böller 2022). In other issue areas, for example foreign aid, antiterror policies, and sanctions against foreign adversaries, bipartisan cooperation proved to be more resilient (Tama 2018, 2020).Footnote 3 Third, ideological polarization among legislators has been identified as a key source of declining bipartisanship (Hildebrandt et al. 2013; Jeong and Quirk 2019). This means that members of Congress hold relatively stable ideological views that inform their policy decisions. Fourth, research on foreign policy in Congress has recently highlighted the emergence of unusual coalitions, for example between left-wing Democrats and libertarian Republicans criticizing presidential infringements on congressional war powers (Müller 2020), and cross-partisan coalitions in favor of trade agreements (Friedrichs 2022).

In view of the state of the art and the insights on polarization in foreign and security policy, it is possible to develop specific hypotheses guiding the subsequent analysis. Given the focus of this article on the role of Republicans in Congress during the Trump presidency, the aim is to identify plausible mechanisms and motives for members of Congress to position themselves vis à vis the president. Three factors seem particularly important, given the previous findings in the literature.

First, the standard model of politics in Congress suggests that electoral concerns are important for rational actors within the legislative branch (see Mayhew 2004). After all, members of the House of Representatives face short electoral cycles (i.e., 2‑year terms), and Senators, despite serving longer terms of 6 years, still depend on their constituency. Therefore, we should expect legislators to represent the majority interests of their voters. At the same time, this responsiveness depends on the extent of majority interests (unclear majorities provide more leeway for MoC), the salience of an issue, and the partisan divide (MoC may focus on representing their core partisan base) (see Foyle 2017; Busby and Monten 2012). The president also factors into electoral concerns. Opposing the president may be electorally dangerous for members of the president’s party in Congress, in particular on foreign policy, where the executive has higher control over the agenda (see Howell and Pevehouse 2005, p. 216; Villalobos and Sirin 2012, p. 36).

Second, as previous research has demonstrated, foreign and security policy choices are influenced by partisan ideology (see Lewis 2017; Busby et al. 2020). In some policy areas, parties have developed distinct profiles, which MoC may adhere to even if public preferences shift. Regarding international issues, this applies, for example, to the support for the military and military means of foreign policy among Republicans (see Dueck 2010), or to the support for human rights issues among Democrats (see Kotb and Jeong 2021). Remnants of bipartisanship, on the other hand, can be explained by converging ideological views and shared definitions of national interests and threat perceptions, which in turn inform acceptable policies (for instance, regarding adversaries or antiterror operations; see Böller and Müller 2018).

Third, executive–legislative relations are structured by the institutional setting (see Homan and LaDeur 2021). While conventional wisdom holds that presidents dominate foreign policy decision-making (see Peterson 1994), Congress possesses various avenues of influence in foreign policy (see Scott and Carter 2002). This includes, for instance, congressional war powers, the Senate’s role in the advice and consent process for international treaties, and direct legislative influence through specific resolutions and the budget process. However, the availability of legislative tools differs across policy areas (see Lindsay and Ripley 1994). For example, the “power of the purse” is a strong tool to exert direct influence on the defense or international affairs budget. In contrast, other policy fields, for example crisis policy (such as military interventions) and strategic decisions (such as nuclear strategy), are dominated by the executive branch to a larger degree. Here, Congress may set limits and influence long-term strategies or use its oversight authority to scrutinize and contest the president, but it is less capable of influencing (or stopping) short-term policy decisions by the president.

Taken together, these factors allow us to develop two sets of core hypotheses and one conditional hypothesis regarding the behavior of GOP members of Congress on international issues.

Hypothesis 1a:

Republican support for Trump’s foreign policy was strong on issues that were ideologically divisive between Democrats and the GOP (partisan ideology),

Hypothesis 1b:

Republican support for Trump’s foreign policy was strong where Trump’s position represented the preferences of GOP voters (electoral concerns).

What follows from these hypotheses is that Republicans supported Trump’s anti-internationalist “America First” doctrine on issues that have been long-contested under previous Democratic administrations and where the Republican Party establishment and base were united, producing a convergence between Trump and traditional GOP positions.

Hypothesis 2a:

Republican support for Trump’s foreign policies was low on issues that contradicted traditional ideological positions regarding vital U.S. national interests (partisan ideology).

Hypothesis 2b:

Republican support for Trump’s foreign policies was low on issues where Trump’s positions were at odds with core constituency interests (electoral concerns).

The second set of hypotheses suggests that establishment Republicans may oppose some of Trump’s most anti-internationalist policies. This pertains in particular to policies that threatened perceived core national security interests or where members of Congress did not have to fear electoral consequences (e.g., because Trump’s proposals were unpopular, even among Republican voters).

The last conditional hypothesis concerns the institutional setting.

Hypothesis 3:

Republican positioning on Trump’s foreign policy depends on institutional avenues of influence, with higher leverage on structural policy fields (e.g., budget, sanctions) and lower influence on crisis policies (e.g., military interventions) and strategic issues (e.g., arms control).

The empirical part of the article will probe the plausibility of the hypotheses with an analysis of the broader voting patterns on the one hand and a qualitative case study on two policy issues (foreign aid and arms control) on the other hand.

3 Less Polarized than Expected: Voting Patterns on Foreign and Security Policy

Roll call votes in Congress provide the opportunity to investigate the broader patterns of partisan alignment across issues over time. It should be noted, however, that the focus on roll call votes may overestimate the extent of polarization because it excludes unrecorded votes, which were presumably less controversial (see Bryan and Tama 2022, p. 8). Mindful of this limitation, the first step of the empirical analysis investigates voting records in the House and Senate to grasp the development of contestation in U.S. foreign policy on the legislative level.

For this purpose, I make use of the Comparative Agendas Project (2022) dataset, which in turn relies on Voteview data (Lewis et al. 2022) and which includes a coding for policy areas. Considering the policy issues of defense (e.g., alliances, military interventions), foreign trade (e.g., trade agreements), and international affairs (e.g., foreign aid, sanctions) as “international” allows us to compare the voting records with all other issues (“domestic”). I focus on the post–Cold War era (since 1991) and calculate the average Agreement Index (AI) as introduced by Hix et al. (2007). Ranging from 0 to 1, the score equals 1 if all members of the legislature vote the same way. The score equals 0 if one-third each votes “yes,” “no,” and abstains. Using the AI instead of other indicators, such as bipartisanship (Kupchan and Trubowitz 2007) or the Rice Index, has the advantage of offering a score that can then also be used to compare the U.S. Congress to other legislatures, as comparative research on parliaments and security policy predominantly uses the AI (see Ostermann and Wagner 2023). However, the AI cannot be considered a direct measurement of polarization (if understood as the growth of extreme positions on the political spectrum), but rather as an indicator of the level of politicization and disagreement within Congress on an issue.

A first look at the data (see Fig. 1) corroborates the thesis of growing politicization on domestic issues (see Theriault 2008; McCarthy et al. 2016) and on international issues (see Trubowitz and Mellow 2011, p. 168). Despite the overall trend,Footnote 4 there are notable fluctuations. Phases of relatively high disagreement during the George H. W. Bush administration and the Obama administration (in particular, 2011–2016) contrast with years of more cohesion on the congressional level, not surprisingly, for example, after 9/11 during the first term of the George W. Bush presidency and also in 2009 (see Fig. 2).

Fig. 1
figure 1

Agreement in Congress on domestic and international issues, 1991–2020. Source: Own analysis, based on data by the Comparative Agendas Project (2022), amended by the author. AI Agreement Index

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Fig. 2
figure 2

Agreement in House and Senate on domestic and international issues, presidential terms 1991–2020. Source: Own analysis, based on data by the Comparative Agendas Project (2022), amended by the author. AI Agreement Index

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If we distinguish between particular areas of international politics, the analysis of the AI reveals some noteworthy shifts in the traditional patterns during the Trump presidency (Table 1). Disagreement was particularly pronounced on defense procurement and human rights compared with previous administrations. Also, roll call votes on military operations and arms control remained controversial—a trend already started during Obama’s presidency. Interestingly, however, during the Trump administration, the level of agreement on the issues of trade, foreign aid, alliances, and international organizations increased against the trend. This could be interpreted as an indication for an overarching consensus among both Democrats and Republicans, who cooperated to fend off some of Trump’s most controversial policies, such as gutting of the foreign aid budget. Similarly, the agreement on alliances may be connected to the attempt to signal support for NATO and other allies in view of Trump’s outspoken criticism against these institutions (see Tama 2021).

Table 1 Average agreement across selected policy fields, presidential terms, 1991–2020
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To investigate this initial finding further, I focus more specifically on the Obama and Trump years, and here on the “key votes” in the Senate. The key votes are coded by experts of Congressional Quarterly based on whether votes presented “a matter of controversy, of presidential or political power, or a matter of potentially great impact on the nation” (Rollcall 2020). There are two arguments to justify this selection. First, the Senate has a more consequential role in foreign and security policy than the House, given its treaty powers and the traditional weight of its international affairs–related committees (Foreign Relations and Armed Services). Second, one criticism against using broad voting record analysis is that the records are skewed by the much more numerous votes on other matters (for example, on various mundane amendments and procedural votes). Therefore, focusing on the most important votes will yield different, and presumably more indicative, results.

The resulting dataset includes 97 key votes for the Obama administration and 33 during the Trump presidency. For this dataset, I use bipartisanship as an indicator for the level of disagreement, defined as a vote in which the majority of party A votes in the same direction as the majority of party B. The dataset was also augmented with a coding for the presidential position on each key vote in order to understand whether Congress supported or rejected a presidential position.Footnote 5

The analysis (Table 2) produces several relevant findings: First, bipartisanship on foreign policy issues was more frequent than on domestic issues. Second, while the level of bipartisanship on domestic issues from Obama to Trump declined considerably, from 20% to 12.5%, bipartisanship on international issues was more frequent in the Senate under Trump. An astonishing 55.6% of all key foreign and security policy votes in the Senate during the 115th and 116th Congress were bipartisan.

Table 2 Analysis of key votes in the Senate, 2009–2021, 111th–116th congressional terms
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Yet, as Tama (2021) has argued, the traditional perspective of foreign policy bipartisanship as an expression of overwhelming support for the president by both parties in Congress may not present the full picture. Indeed, considering the policy direction of the key votes in the Senate reveals that the increase in bipartisanship during the Trump presidency was rather unusual. Thus, a third relevant finding is that during the Trump presidency, only one case of pro-presidential bipartisanship can be detected. In three cases, a bipartisan majority formed against the president. Furthermore, in four cases, Trump lost a key foreign policy vote (i.e., the majority voted against his declared policy preference) due to an unusual alliance between the majority of Democratic Senators and a minority of Republicans (what can be termed as “cross-partisanship”). In contrast, President Obama lost only one key vote due to “anti-presidential bipartisanship” (Tama 2021), the Justice Against Sponsors of Terrorism Act.Footnote 6 In addition, Congress defied Obama regarding the fiscal year 2016 National Defense Authorization Act due to cross-partisanship. Among other reasons, Obama objected to the bill because it entailed the restriction of funds for the president’s plan to close the Guantanamo detention facility (see Poplin 2015).

Upon closer inspection, the only case of pro-presidential bipartisanship in the Senate during Trump’s presidency was the passage of H.R. 601 in September 2017, a package that included funding for disaster relief and defense purposes, after a deal was struck with Democrats.

Key votes against Trump’s declared preferences pertained to sanction policy, military interventions, and defense policy issues. Regarding sanctions, lawmakers clearly opposed Trump’s initial intent to soften the sanctions regime against Russia. H.R. 3334 passed both chambers of Congress in July 2017 with veto-proof majorities (Senate: 98:2; House: 419:3) to reaffirm and expand the sanctions against Russia and preempt Trump’s rapprochement efforts with Putin. This assertiveness seems connected to an overarching consensus regarding the threat posed by Russia to U.S. national security. While the final vote was almost unanimous in both chambers, it is notable that the legislative process was spearheaded by Democrats as well as Republicans. The most active Republicans in the Senate here included John McCain (R-AZ), Lindsey Graham (R-SC), and Bob Corker (R-TN), who can be described as Republican establishment (see Böller and Herr 2020). The Senate later also passed—with 11 Republicans joining Democrats—a nonbinding resolution criticizing Trump’s maneuvers to circumvent the sanctions (S.J. Res. 2).

The second major area of congressional opposition against President Trump’s foreign policy concerns military interventions. Here, a cross-partisan coalition formed to criticize U.S. support for the Saudi-led alliance in the Yemen civil war; S.J. Res. 54 and S.J. Res. 7 aimed at limiting U.S. involvement. This attempt ultimately failed due to Trump’s veto, which this coalition could not override. A bipartisan majority, on the other hand, expressed discontent with Trump’s proposed withdrawal from Syria. This measure (S. 1 - Strengthening America’s Security in the Middle East Act of 2019) was, nota bene, non-binding. Several aspects of the politics of military interventions under Trump are insightful. On the one hand, the voting records indicate division within the GOP regarding Yemen (and also Iran),Footnote 7 where most Republicans sided with their president, and only a small group opposed Trump. On the other hand, in line with the argument that bipartisanship depends on shared perceptions of national interests, Trump’s sudden shift in antiterror operations regarding Syria provoked a broad outcry in Congress, as the shift was seen as harmful to U.S. security (see O’Brian 2019). Yet this policy area also underscores the relevance of the institutional perspective: Congress’ influence on Trump’s decisions was also limited due to the ineffectiveness of congressional war powers.Footnote 8

In the area of defense, the Senate disapproved of Trump’s weapons sale to Saudi Arabia (S.J. Res. 36), in line with previous criticism against the war in Yemen, but the cross-partisan coalition failed to override the president’s veto. In contrast, Congress was successful in overriding Trump’s veto against H.R. 6395, the defense authorization bill for the fiscal year of 2021. Among other reasons, Trump opposed the bill because it sought to limit his ability to implement the withdrawal of troops from Afghanistan, as well as from Germany and South Korea. Here, a veto-proof bipartisan majority signaled its intention to uphold U.S. commitments to its allies, an issue area where Republicans and Democrats view vital security interests at stake (see Tama 2021, p. 30).

To summarize this first step of the analysis, contestation over foreign and security policy increased over time, although to a small degree and with fluctuations between administrations. In particular, during the Trump administration, bipartisanship on international issues increased, gauged by key votes in the Senate. At least on some policy issues, including military interventions, relations with Russia, and the defense budget, lawmakers aimed to provide a check on Trump’s policies (see Tama 2021, pp. 25–35).

The analysis also underscores the puzzle of the variance in congressional responses on foreign and security policies. Areas of anti-presidential bipartisanship stand in contrast to issues such as arms control, where Congress remained largely silent in view of Trump’s focused attempt to dismantle key international agreements. In the following section, I therefore aim to analyze the sources of this variance.

4 Between Defiance and Support: Congress and the Politics of Foreign Aid and Arms Control Under Trump

In order to understand the puzzling variance in congressional positioning toward Trump’s foreign and security policies, I will present two case vignettes in a comparative perspective: foreign aid and arms control. The case selection is based on two arguments: First, to understand the variance, cases of congressional assertiveness as well as acquiescence need to be included. As the previous section indicated, foreign aid policies have been contested, while arms control policies received either support or were met with silence from Capitol Hill. Second, the case selection aims to focus on policy fields with varying opportunities for congressional involvement in foreign affairs, due to their institutional setting. Whereas foreign aid pertains to the structural policy field with high chances of congressional influence, arms control policies are part of the strategic policy area with comparatively lower institutional leverage for Congress (Lindsay and Ripley 1994).

4.1 Foreign Aid: Bipartisan Opposition Against Budget Cuts

Putting American interests first has been a core slogan of Trump’s foreign policy doctrine, both as candidate and president. In his major foreign policy speech during the campaign in 2016, Trump described his policy: “We’re rebuilding other countries while weakening our own. Ending the theft of American jobs will give us resources we need to rebuild our military, which has to happen and regain our financial independence and strength” (Trump cited in The New York Times 2016). The stated rationale behind this doctrine was to prioritize economic welfare and military strength while avoiding spending taxpayers’ money for purposes beyond narrowly defined national interests, such as the promotion of democracy and liberal values abroad (see Lacatus 2021).

Trump’s statements and proposals followed up on his campaign promises. Repeatedly throughout his presidency, Trump intended to slash funding for foreign assistance programs by between 20% and 30% according to presidential funding requests (see CRS 2021). The budgetary cuts specifically targeted programs related to climate change, countries in Central America (presumably to force them to change their immigration policies), and HIV/AIDS programs (see CRS 2021, pp. 1 and 16), thus reflecting an ideological orientation. Furthermore, Trump sought to redirect the remaining funds to supposedly friendly states. The latter strategy reflected Trump’s transactionalist orientation. Accordingly, the distribution of aid should be based on U.S.-supportive voting behavior in international institutions, as indicated in the 2018 State of the Union Address (Trump White House 2018; see Igoe 2020).

However, a bipartisan majority among Democrats and Republicans in Congress fought back and defended large parts of the existing funding and programs. In particular, presidential attempts to cut the funding for foreign aid remained unsuccessful. As Fig. 3 shows, in each year of the Trump administration (starting with the budget process for fiscal year 2018 in 2017), the funds appropriated by Congress exceeded the president’s initial budget request. Thus, the overall appropriated budget for international development and bilateral security assistance remained stable compared to the last year of the Obama administration. It is not unusual that presidential budget requests and appropriated funds differ—for example, due to new emergencies or to protracted budgetary negotiations. In the case of Trump, the differences clearly resulted from the 45th president’s declared goal to cut funding and Congressʼs outright opposition to that (see Tama 2021, pp. 33–35).

Fig. 3
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Funding for foreign assistance (USD, billions, fiscal years). Reported data for fiscal year 2021 incomplete. Source: Own depiction based on data by USAID (2022)

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Already Trump’s first budget plan in 2017 met bipartisan opposition in Congress regarding foreign aid. In June 2017 during congressional hearings, Senator Graham, for example, bemoaned, “this budget request is radical and reckless when it comes to soft power” (cited in Saldinger 2017). Graham, renowned as a foreign policy hawk (see Martin 2013) and indicative of Republican establishment in foreign and security policy, maintained that soft power was “just as important as any military power we have” (cited in Saldinger 2017).

Similarly, in 2018, House Foreign Affairs Committee chairman Ed Royce (R-CA) declared his opposition to Trump’s budget cuts: “A strong, bipartisan coalition in Congress has already acted once to stop deep cuts to the State Department and Agency for International Development that would have undermined our national security … This year, we will act again” (cited in Toosi 2018). Time and time again, a bipartisan opposition formed against the president to defeat plans perceived as “detrimental to our national security.”Footnote 9

The Trump administration’s foreign aid agenda was also contested outside Congress. Nongovernmental organizations, former officials of Republican administrations, and a group of former generals and admirals protested the budget plans and stated their conviction that “elevating and strengthening diplomacy and development alongside defense are critical to keeping America safe” (cited in U.S. Global Leadership Coalition 2017). Even conservative think tanks, such as Rand and Brookings, denounced the plans as dangerous to U.S. security interests (Cohen 2020; Ingram 2017). What these statements from within and outside Congress have in common is a legitimization based on a definition of national interests that is broader than Trump’s narrow “America First” doctrine.

Beyond the defended budget, congressional assertiveness also led to intensified investigation and oversight—most notably in the case of Trump’s first impeachment due to withheld security assistance funding for Ukraine—and to reasserted congressional authority over the foreign aid programs (see CRS 2021). However, Trump’s attempts to reform the foreign assistance programs were not without effects. The Trump administration used unilateral executive measures to circumvent congressional limits and to withheld funds to multilateral institutions, such as the Human Rights Council, the United Nations Population Fund, and the World Health Organization (see CRS 2021, pp. 2–3; Regilme 2022, pp. 10–19).

Public opinion polls do not indicate that MoC received clear electoral signals to position themselves in this policy field. On the one hand, the U.S. public in general seems skeptical of economic aid to other countries. When asked in 2017 whether to increase, cut, or keep federal spending for this purpose, 50% of respondents favored cuts, 32% continuance, and 10% expansion. On the other hand, questions pertaining to specific programs (e.g., food and medical assistance, economic development) reveal that majorities of both Republicans and Democrats support foreign aid, although Democrats show higher levels of support (CCGA 2017a). In addition, foreign aid topics generally are less salient to voters compared with other foreign policy issues (Hurst et al. 2017, p. 452).

In sum, this case vignette lends support for Hypothesis 1a, as we find bipartisan agreement rather than division. Hypothesis 2a is also corroborated, as Trump’s proposals contradicted long-term positions held by Republicans—and in this case, in bipartisan fashion, also Democrats. As electoral incentives do not indicate a clear direction, Hypothesis 2b is rejected.

Seen from an institutional perspective, Congress possessed constitutionally mandated powers to check the president’s policy preferences. The policy field can be classified as a “structural” environment (Lindsay and Ripley 1994, p. 10). Here, the power over the federal budget and the oversight authority to investigate and review institutional reforms provide Congress with enough leverage to assert itself against the president. This finding is in line with Hypothesis 3 regarding the institutional setting. Combined with the bipartisan agreement between Republicans and Democrats, the basic tenets of U.S. foreign aid policies withstood Trump’s agenda.

4.2 Arms Control: Ideological Division Fueling Support for “America First”

The withdrawal from international arms control agreements was one of Trump’s signature elements of his “America First” platform. This policy strategy also has a clear ideological orientation and connection to core “Trumpism,” as it frees the United States from binding commitments, conforms to Trump’s transactionalist orientation, and implements a narrow focus on national security interests. To be sure, other presidents before Trump have at times resorted to unilateralism and have dissolved international commitments (see G.W. Bush’s withdrawal from the Anti-Ballistic Missile Treaty in 2002; Kubbig 2005). However, Trump’s actions had a broader scope, including not only the Iran nuclear deal but also the Intermediate-Range Nuclear Forces (INF) Treaty, the Open Skies Treaty, and the Arms Trade Treaty.Footnote 10 Trump was also more consistent than Bush in this regard, as the latter also initiated new arms control agreements, such as the Strategic Offensive Reduction Treaty (SORT) and the International Code of Conduct Against Ballistic Missile Proliferation (ICOC).

Despite being a signature element of Trump’s foreign policy doctrine, the president’s treaty politics cannot be seen as an invention of Trump. Rather, there are sources of inspiration among Republicans in Congress who politicized the issue of arms control well before Trump (see Kubbig 2005; Kühn 2019). During the Obama administration, arms control and non-proliferation policies provoked controversies between Democrats and Republicans. Obama could barely secure the necessary support from Republican senators for the ratification of the New START Treaty in 2010—a traditional bilateral arms control agreement, similar to those previously supported by strong bipartisanship (see Kreps et al. 2018). Polarization further infected this policy field in the wake of the negotiations on the Iran nuclear deal. This agreement was fiercely contested by Republicans in Congress (see Friedrichs 2021). The final vote on the Joint Comprehensive Plan of Action (JCPOA) in September 2015 illustrates the partisan division in this debate. Only four Democrats voted together with all 54 Republicans in the Senate in favor of a Joint Resolution of Disapproval against the deal. The attempt to stop the implementation of the executive agreement thus barely failed (see Schreyer and Wilzewski 2015, p. 3).Footnote 11 However, the protracted discussion and continuous attacks politicized the arms control negotiations. In this context, presidential candidate Trump joined Republicans in Congress and frequently denounced the agreement, criticizing it as “terrible” and “horrible” (cited in Trump Twitter Archive 2022).

The INF Treaty was also subject to criticism in Congress before Trump. Even the Obama administration publicly declared in 2014 that Russia is in violation of the treaty (see Department of State 2017). However, President Obama aimed at resolving the differences with Russia bilaterally and sought to preserve the treaty. This position was contested by Republicans in the 113th and 114th Congresses. Marco Rubio (R-FL), for example, introduced a resolution in 2014 that urged the administration to hold Russia accountable for its treaty violation (Rubio 2014). Similarly, Mike Rogers (R-AL), then chairman of the subcommittee on strategic forces, demanded in 2015 that the United States should not “be unilaterally bound by any treaty” while Russia is cheating (cited in Gertz 2015). This criticism was also shared by conservative think tanks, for example the Heritage Foundation, and supplemented by demands to modernize the U.S. nuclear arsenal (see Heinrichs 2014). Thus, unsurprisingly, leading Republicans, including ranking member of the House Foreign Affairs Committee Mike McCaul (TX), applauded Trump’s INF withdrawal decision (see Toosi et al. 2019).

Republican senators and representatives not only took aim at the INF Treaty but also attacked the multilateral Open Skies Treaty, even before Trump announced his intention to abandon the treaty (see Richter 2020). S.Res. 388, spearheaded by Ted Cruz (R-TX) and Tom Cotton (R-AR) demanded to terminate U.S. participation in the Open Skies Treaty. The resolution accused Russia of violating the agreement and pointed out that the United States “does not gain significant additional intelligence from participating in the Open Skies Treaty” (see Cotton 2019). The response on Capitol Hill to terminate participation in the Open Skies Treaty similarly followed partisan lines. While Senator Bob Menendez (D-NJ) denounced the withdrawal as “reckless,” Cruz and Cotton praised the president’s decision (Gould et al. 2020).

Ideological agreement thus seems to be the primary explanatory factor for the support among Republicans for Trump’s arms control policy (support for Hypothesis 1a). Public opinion surveys suggest that there were few clear electoral incentives for GOP members of Congress (contradicting Hypothesis 1b). Voters do not seem to have prioritized arms control, whereas China and international terrorism are perceived as the primary threats among Republican voters (CCGA 2020, p. 5). Opinion polls on the question of the Iran nuclear deal also do not suggest a clear electoral incentive. In 2017, Republican supporters were split in their assessment of the JCPOA (see CCGA 2017b). However, a majority of 73% among self-identified Republicans supported Trump’s INF Treaty withdrawal (CCGA 2019).

Seen from an institutional perspective, the Senate possesses veto powers over treaty ratification, may signal discontent over policies in the area of arms control, and can block new treaties.Footnote 12 However, the Senate and Congress in general have only a few options to stop unilateral presidential decisions, if, as in Trump’s case, the president opts to withdraw from a treaty.Footnote 13 As this case vignette suggests, GOP Senators supported Trump’s arms control agenda because it aligned with already developed Republican positions in this policy field.

5 Conclusion

While there is no shortage of analyses on Trump’s foreign and security policies (e.g., Lacatus 2021; Löfflmann 2019; Ashbee and Hurst 2020), there has been a void in understanding the role of Republican senators and representatives in particular within International Relations and foreign policy analysis. In this article, I have sought to reduce this gap and provide answers to the puzzling variance of assertiveness and acquiescence among Republican members of Congress toward Trump’s “America First” policies. Empirically, my paper argued that Republicans opposed some of Trump’s anti-internationalist policies, in particular those that seemed to threaten core national interests. In some cases, President Trump faced a bipartisan coalition that put roadblocks on the paths toward the implementation of “America First,” such as regarding sanction policies or the foreign aid budget. These efforts were spearheaded by established GOP senators who tried to defend traditional policy positions. At the same time, Republicans supported Trump on issues such as arms control and non-proliferation policies. The identified source of this alignment is ideological agreement. Republicans in Congress already favored a unilateral reorientation in this policy field under the Obama administration, and they were staunch opponents of the Iran nuclear deal. The impact of congressional criticism directed at Trump also depended on institutional avenues of influence: On foreign aid (and sanctions), Congress was able to use its power of the purse to pass binding legislation contradicting presidential positions. Against Trump’s treaty withdrawal strategies, on the other hand, Congress remained powerless, despite the fact that the president’s sole authority to dissolve treaties is at least questionable, even though such unilateral withdrawals are not unprecedented.Footnote 14

While the empirical focus of this article has been congressional reactions to Trump, the results discussed here have relevant implications for other aspects of international affairs and domestic politics, too.

First, regarding the intrapartisan dynamics and the question of Trump’s dominance of the GOP (as also discussed in other articles in this special issue), this case study suggests that there is substantial division and intraparty contestation against “Trumpism” (see Smeltz and Tama 2021). It also highlights at least partial resilience of traditional conservative policies, albeit to varying degrees.

Second, the results discussed in this article are also relevant from an institutional perspective. Congress can check the president in foreign policy and is not as powerless as sometimes portrayed (see Mann and Ornstein 2006). However, the degree of this role as a counterbalance depends on institutional avenues of influence. Whereas congressional entrepreneurs were able to shield foreign aid policies via their control over the budget, unilateral policies on arms control faced little congressional resistance (even from the minority), or they resulted in symbolic contestation only (see the criticism on military intervention policies), also because of constrained institutional avenues of influence.

Third, congressional engagement also affects the outcome of foreign and security policy on the international level and is thus relevant for transatlantic partners as well. Trubowitz and Harris (2019, p. 619) have, for instance, argued that the decline in bipartisan agreement on foreign affairs reduces the “usable power available” to sustain the costly U.S. leadership role. My article provides a qualification to this argument and the broader literature on polarization in foreign and security policy (see also Friedrichs and Tama 2022). As the empirical analysis shows, the level of disagreement over foreign policy varies across policy fields. Furthermore, anti-presidential coalitions (see also Homan and Lantis 2020; Bryan and Tama 2022) may break the standard operating mode of partisan politics to stop policies that are perceived as harmful to national interests, when such perceptions are shared by a majority of Republicans and Democrats in Congress. In fact, Congress worked to cushion the effects of Trump’s “America First” agenda, for example by protecting important elements of U.S. soft power with the continued funding of the foreign aid budget. Despite the overall influence of Trump within the Republican Party, a more or less stubborn establishment was able to defend the remnants of an internationalist consensus.

Part of this consensus also remains intact regarding security alliances. This enabled Trump’s successor, President Joe Biden, to provide military aid for Ukraine’s defense against Russia, supported by a bipartisan coalition in Congress, although to varying degrees (see Gramer 2022).Footnote 15 At the same time, there are important caveats regarding the remnants of the internationalist consensus in Washington, D.C.: On the one hand, polarization is affecting previously bipartisan policy fields, such as arms control, where Trump—supported by Republicans in Congress—was able to dissolve important international agreements. The ability to enter credible commitments in this policy area hence continues to be weakened (see Schultz 2017, p. 20). On the other hand, the contestation of presidential foreign policy results in mixed signals from different domestic actors, hurting the capacity of the United States to clearly communicate its preferences toward adversaries and allies.

Even if allies are reassured by congressional foreign policy activism, international reactions are ripe with unintended consequences and miscalculations. It may be argued that hedging strategies by European allies against an imminent withdrawal of its security guarantor were limited because foreign leaders were reassured by Congress of the continued reliability of the United States. However, it is plausible that allies underestimate that U.S. security commitments could be undermined again under a new president, following a doctrine similar to Trump’s. Furthermore, assertiveness on Capitol Hill is limited pursuant to the institutional setting in each policy area, and presidents can use unilateral tools to circumvent congressional checks on their foreign policy.