Divisive, polarising, or energising? Primary election competition and candidate performance in U.S. congressional elections

How do primary elections influence general election outcomes? The conventional wisdom in American Politics predicts a ‘primary penalty’ that harms a party or candidate’s chances of winning the ensuing general election. I present and test an alternative theory inspired by comparative studies of Latin America: primary election competition results in a ‘primary bonus’ which may make candidates more likely to win the general election that follows. Despite potential for polarisation and divisiveness, robust primary competition encourages campaigns to professionalise and mobilise voters, weeds out unfit candidates, and provides a testing ground for messages and policies. Furthermore, the nature of the primary electorate and incumbency advantage may mitigate the proposed sources of the penalty. Analysis of data collected from multiple sources on all U.S. congressional elections (2008–2016) lends strong support to the Primary Bonus hypothesis. Primary elections strengthen candidates for the general election, contrary to extant theories in American politics. This study is the first to find a primary bonus in U.S. congressional elections.