A spatial model of U.S. Senate elections

The importance of primary elections is considered within the context of U.S. Senate elections where senators serve overlapping terms and voters are assumed to balance their two senators against each other. Voters behave strategically in the primaries but convergence to the median position is not achieved except as a knife-edge result. More generally, constraints in the party space prevent the party of the sitting senator from obtaining the median’s preference allowing the opposition party to nominate a candidate further away from the median while still capturing the median voter. Empirical evidence supports the notion that senate divergence is a function of the state primary system.