Many hypothesize that the divergence between Democratic and Republican members of Congress is partly attributable to partisan primary elections. Yet most empirical evidence on the influence of primary elections finds small to no effect on member behavior. I argue that existing designs that compare members elected out of nomination systems with more open rules of access to members elected out of more closed systems rest on the crucial and untested assumption that more closed institutions lead to more polarized primary electorates. With survey opinions, turnout validated to voter files, and an IRT model of ideology, I characterize the preferences of Democratic and Republican primary electorates and general electorates in each House district in 2010 and 2012. To the extent that there is a relationship between primary ideology and closed primary institution, it is in the direction opposite that hypothesized. I then show that the primary electorate diverges from the general electorate in every House district and even from supporters of the party in the general election in almost every district, which is consistent with a centrifugal influence of primary voters. These results suggest that institution of nomination may not have a large influence on the type of voters who turn out, and that some other feature of nominating contests must be implicated in polarized primary voters.