Why primaries? The party's tradeoff between policy and valence

Our theory studies why and when political parties choose to hold competitive primary elections. Party leaders can decide the nomination by granting resources and endorsements to a chosen candidate. Alternatively, they can delegate the candidate selection to the party's rank and file by holding a primary election among multiple candidates. The benefit of a primary is to increase the expected valence of the nominee. Its cost is the ideology that primary voters might induce on the party's policy platform. We find that primary elections are more likely to be used when the potential primary voters are not too moderate and not too extremist. We also find that opposition parties and weak parties benefit from primaries more than incumbent parties and strong parties do. Intriguingly, extremist parties are more likely to adopt primaries than centrist parties are. Contradicting previous research, we find that primaries are more attractive when candidates' skills are less salient for voters than candidates' policies.