Presidential coattails versus the median voter: Senator selection in US elections

We show that senators elected in presidential elections are more ideologically extreme than senators elected in midterm elections. This finding is in contrast to the literature suggesting that voters in presidential elections are more ideologically moderate than voters in midterm elections. To explain this incongruence, we propose a theory of spillover effects in which party labels enable voters to update their beliefs about candidates across contemporaneous races for office: unexpected support for a candidate in one race carries marginal candidates from the same party in other races. Our theory implies that presidential coattails may skew representative government away from the median-voter ideal.