Much of the scholarly interest in critical realignments results from the pivotal role that ordinary citizens play during these periods. By altering their voting behavior, citizens hold political elites accountable and forge non-incremental change in policy outputs. A central question regarding realignments is thus how are citizens changing their behavior to hold elites accountable? Are citizens producing realignments by converting from one party to the opposition? Are previous non-voters becoming mobilized in response to emerging issues or crises? Or are one party’s supporters disproportionately abstaining from voting and altering the partisan balance in the process? This article makes four central contributions to our understanding of these realignment processes, or dynamics. We present a theoretical framework for the analysis of realignment dynamics, based upon the Michigan model of voting and its conception of the normal vote. Where previous dynamics studies have collectively only examined two realignments, we examine the dynamics of all presidential realignments in American electoral history. Where previous studies have often focused on national, sectional, or state levels of analysis, we focus on city- and county-level realignments, a critical advancement for an inherently local-level phenomenon such as critical realignments. Finally, unlike previous studies, we identify the factors that promote particular realignment dynamics. We find that the conversion of active partisans has produced most of the enduring change in voting behavior in the United States, with the relative contribution of different dynamics varying both across time and space. Political factors such as the strength of state and local parties and demographic factors such as changes in the size of local immigrant populations have each favored particular realignment dynamics in American electoral history.