Polarization in U.S. presidential nomination campaigns
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This research presents a theory of political polarization which argues that changes in American society, political culture, institutions, media, and technology combine to create conditions favorable to political polarization at the mass and elite levels through a process known as party sorting. As ideological conservatives sorted into the Republican Party and ideological liberals sorted into the Democratic Party, each party became ideologically homogenous. Homogeneity allows ideological polarization amongst political elites, political activists, and the American electorate to increase because it promotes ideological extremism and discourages ideological moderation through “group think.” Without the presence of liberal Republicans and conservative Democrats to raise alternative viewpoints, to oppose the party’s status quo on issues, and to foster compromise with the opposition party, ideological extremism increases and the two parties diverge ideologically. The dissertation empirically demonstrates two important effects that political polarization is having on the American political system. Analysis of the American electorate reveals a sharp increase in polarization between Republican and Democratic voters over the past decade. The preferences of Republican and Democratic voters are increasingly divergent. The analysis then examines the ideological distribution of all presidential primary candidates since 2000 using ideal point estimation. The analysis reveals that individual primary candidates are becoming more ideologically extreme, creating more ideologically extreme candidate fields. There was a sharp increase in ideological extremism between the 2008 and 2012 Republican contests with many 2012 Republican candidates far to the ideological right of comparable Republican candidates in earlier cycles. By providing empirical evidence of mass level polarization and elite polarization outside of congressional elites, the dissertation makes an important contribution to the political polarization literature.