The Twisted Game Theory of the Tea Party

There's a post from Tom Jensen of PublicPolicyPolling making the case that Obama's problem isn't with liberal Democrats, it's with conservative Democrats. The heart of the argument as to why:

Conservative Democrats are ultimately a bigger threat to Obama's reelection prospects than liberal ones. They don't necessarily make a lot of noise about it when they're unhappy- they just go out and vote for Republicans. Liberals on the other hand really have nowhere to go- they can stay at home or vote for Ralph Nader but ultimately that's just going to get them someone who makes them a lot more unhappy than Obama. It's not a pleasant reality, but in our two party system that's just the way it goes- conservatives definitely have more leverage than liberals within the Democratic coalition and that's why they so often get their way despite their smaller numbers.

This feels right to me, and it's certainly the way things like the Median Voter Theorem are supposed to work in an electoral system set up like ours, i.e. not actually moving both parties to the opinions of the median voter but forcing both parties to be able to make a strong pitch to that median voter. But what I keep wondering is, why on earth doesn't this work on Republicans? Why is it that the conservative Republicans keep having so much more influence, despite the fact that it ought to be the members of a coalition who lie closer to the median of society who have the leverage?

I think it's because the hard-right faction of the Republican base is willing to make a credible threat to be irrational. That is to say, they are willing to nominate candidates who are more conservative than the establishment alternative and who then lose. Theoretically, when they lose their primaries, they are willing to run genuine third-party candidates. Liberals, after flirting with this irrationality in 2000, have learned our lesson, so a threat to be irrational isn't particularly compelling. We won't make it, because we all know that the result is too horrible to be contemplated. But the Tea Partiers have shown no particular preference for having a moderate Republican in office than having a Democrat in office. And that gives them power.