Incremental Polarization

This book provides a unified spatial model of legislative elections, parties, and roll call voting to address three primary questions: why do legislators adopt extreme positions, how do they win given their extremism, and what role do parties play in promoting polarization? The book links spatial models of elections to spatial models of roll call voting in the legislature, and suggests that the key to understanding polarization is to reverse the order of conventional models and place the legislative session before the election because legislators adopt positions in the policy space, extreme or otherwise, through the incremental process of casting roll call votes. Linking a spatial model of an election to a model of roll call voting, the book derives the following. When a legislative caucus is ideologically homogeneous, electorally diverse, and policy motivated, it will empower party leaders to solve the collective action problem of sincere voting by counterbalancing members’ electoral pressure to vote as centrists. The result is that the caucus achieves policy goals at the cost of some electoral security, but agenda paradoxes minimize the electoral damage done, so most incumbents win re-election anyway at only slightly diminished margins. This model explains the development of polarization in the House of Representatives throughout the post–World War II period, and key votes on legislation such as the Affordable Care Act. Moreover, even the unusual politics within the Republican Party during the divided government period from 2011 through 2016 follow naturally from extensions of the model.