Party Polarization in Legislatures with Office-Motivated Candidates

We develop a theory of legislative competition in which voters care about local candidate valence and national party positions that are determined by the parties’ median legislators. As long as election outcomes are sufficiently predictable, the only stable equilibria exhibit policy divergence between the parties. If the degree of uncertainty about election outcomes decreases, and if voters place less weight on local candidates’ valence, polarization between the parties increases. Furthermore, a systematic electoral shock makes the party favored by the shock more moderate, while the disadvantaged party becomes more extreme. Finally, we examine data on state elections and the ideological positions of state legislatures and find patterns that are consistent with key predictions of our model.