Abstract
The chapter examines the relationship between the increased polarization of American political parties and the candidate nomination process. It links a growing insurgency in the Republican Party, in part, to the unique American system of primary elections. Using a variety of data sources, it shows that Republican primaries in particular have become a home for a large cohort of primary voters who tend to view politics in black-and-white terms, holding purist beliefs on which they are unwilling to compromise. These same voters believe strongly in procedural populism, meaning they resist any vetting by party professionals in the selection process, preferring that only Republican voters select candidates in primary elections. Through primary voting and other forms of engagement these populist voters exercise disproportionate influence on the direction of the party issue agenda. Their attitudes and behaviors incentivize the entry of insurgent candidates who benefit from a campaign finance system that allows independent spending from ideologically extreme groups. We do not observe these patterns in such stark terms on the Democratic side, helping us isolate some of the unique factors affecting the modern Republican Party. Given the populists impulses of core Republican voters, we expect strong resistance to institutional changes within the Party that might strengthen the gatekeeping role of party professionals who would prefer establishment-oriented conservatives. The voters’ anti-pluralist attitudes reflect an understanding of democratic politics that appears to leave little room for elite discretion or accommodation with other interests in the polity.