So after switching parties to avoid a primary challenge from Pat Toomey, Arlen Specter is facing a primary challenge from his left . . . and may be behind Toomey in the polls. (Yes, the biggest gap is Rasmussen, but other polls show the same thing, with a smaller gap.)

This has gotten me thinking about Jim Jeffords, who switched parties to much fanfare, even writing a memoir with the gag-a-rific title of "My Declaration of Independence"--but got hammered when Republicans re-took the Senate.

I wonder: is this sort of high-profile party-switching always doomed? I don't mean the more garden variety switches, where some liberal Republican or conservative Democrat finally decides to join his ideological brethren. I mean the kind of splendiferous gesture that gives the other party considerably more power.

This is not because I think it is morally wrong, or any such nonsense. Rather, party switchers who do that sort of thing are taking a big risk; if the other party regains power, they will make the payback sweet and slow. So politicians only hand power to the party they are joining when that party looks particularly strong (or at least, likely to get much stronger).

The problem with that is that parties are apt to look the strongest right before the worm turns. What sorts of things make a party look strong? Longevity, large numbers, a public angry at the other party. But parties that have been in power for a while, who have a lot of members, are parties that are apt to have to take responsibility for anything that goes wrong. Voters may be wearying of them. Meanwhile, anger at politicians tends to be fierce but temporary; it takes a crisis like the Civil War or the Great Depression to make a permanent majority.

I suspect that there may be a political version of the winner's curse: the tendency of auctions to be won by the person who is most overoptimistic about the value of the object for sale. Similarly, perhaps people only switch parties in such a spectacular fashion if they have unrealistic expectations for the permanence of the coalition they are joining.

But I'm working from a very small sample here. Thoughts?

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