The Electoral Causes of Party Polarization in Congress

Party polarization has fundamentally altered the political landscape in the United States. For good or ill, it has increased the contentiousness of elections, it has changed the conduct of government business, and it potentially affects the quality of representation many citizens receive in Congress. Nonetheless, explanations of its emergence remain incomplete, often being time-bound or region-bound, and most ignore the possibility that party strategy lies at the heart of this development. In response to this lacuna, in this dissertation I present evidence that over the past thirty years party leaders have helped bring about party polarization in Congress in the way they have distributed party campaign funds to candidates. I find party leaders helped make congressional caucuses more ideologically homogeneous over time by providing party support to ideological challengers and open-seat contestants and thereby significantly improving their likelihood of gaining seats; by targeting resources toward races against moderate incumbents of the opposite party with great success; and by providing party monies to protect their own moderate incumbents at the expense of making those incumbents more vulnerable to seat-challenges and targeting by the other party. These allocation decisions contributed to the replacement of moderates in Congress with ideological new members and made the party caucuses in Congress more ideologically unified and distinctive over time.