When will incumbents avoid a primary challenge? Aggregation of partial information about candidates' valence

Abstract

When can a party insider feel safe from an outside challenge for a future nomination? In most countries, parties can choose whether to hold a primary election where the rank-and-file members take a vote, or to allow party leaders to directly appoint an insider candidate of their liking. The cost of primaries forces candidates to drift away from the party leader's policy preferences in order to cater to primary voters. This paper postulates a benefit: primary elections can reveal information about the electability of potential candidates. I refine the formal model in Serra (2011) by making the realistic assumption that such information is revealed partially rather than fully. A signaling mechanism is introduced whereby candidates send noisy information that is used by primary voters to update their beliefs. This leads to surprising insights about the behavior of primary voters: under some circumstances they will use the information provided by primary campaigns, but under other circumstances, they will choose to completely ignore such information. In addition, the results predict that popular incumbents will not be challenged in a primary election, which is consistent with empirical observation. Finally, a prescription for parties is to allow their primaries to be tough given that stiff competition will improve the expected ability of the nominee.