Geography and Polarization1

the roll-call data collection effort. We also thank the following for exemplary research assistance: Steve Rogers, Michael Barber, and Chad Levinson. Using new data on roll-call votes and public opinion in U.S. state legislative districts, we ex-plain how ideological polarization within districts can lead to legislative polarization. Many of the seemingly “moderate ” districts in suburbs and smaller cities that switch hands be-tween Democrats and Republicans are internally polarized. The ideological distance be-tween Democrats and Republicans within these districts is often greater than the distance between liberal cities and conservative rural areas. We present a theoretical model in which intra-district ideological polarization causes candidates to be uncertain about the ideological location of the median voter, thereby reducing their incentives for platform moderation. We then demonstrate that in otherwise identical districts, the difference in roll-call voting be-havior between Democratic and Republican state legislators is a function of within-district ideological heterogeneity. Accounting for the subtleties of political geography can help ex-plain the juxtaposition of a polarized legislature and a moderate mass public. Our analysis encourages skepticism about redistricting reforms that aim to cure polarization by creating more heterogeneous districts