Republicans are going to gain a lot of seats in the midterm elections. The big question is why. Political punditry has been saturated with arguments interpreting this result as a verdict of sorts on the Obama administration. Liberals are interpreting the incipient GOP win on poor communication or perhaps timid policies by the Democrats. Conservatives are interpreting it as the natural punishment for a party that moved too far left. (The mainstream media is taking up a softer version of this "center-right country" argument -- see the Hill's editorial arguing that "Democrats may have failed to learn lessons about overreach," an opinion which is noteworthy because that publication editorializes only when it can safely confirm the conventional wisdom.)

It's certainly legitimate to question the policies or the tactics of the Obama administration. But in order to have that conversation, you need to begin with a baseline expectation. What sort of performance should we expect normally? Clearly, in the current environment, it's not rational to expect the majority party to escape any losses whatsoever. If you want to blame the Democrats' loss on bad messaging or wimpy policies or rampaging socialism, then you need to establish how you'd expect them to do given normal messaging and policies.

Political scientist Douglass Hibbs has a model of the election. It takes account of three factors:

1. The presence of a midterm election, which generally results in losses for the president's party.

2. The incumbent party's "exposure" -- the more seats you hold, the deeper into hostile territory you're stretched, and the easier it is to lose seats.