Yesterday I wondered why progressives are supporting a primary challenger against Blanche Lincoln who, after all, voted for health care reform and hails from a very conservative state. Matthew Yglesias replies that the answer is, because they can:

To mount a challenge from the left, you really need two things. One is you need progressive activists and institutions ready to back the challenger. And the other is that you need a challenger. And what Arkansas has is a solid challenger in the form of an incumbent Lieutenant Governor—exactly the sort of person who would beat a sitting Senator. It’s definitely true that in the abstract Lincoln is far from the worst offender in terms of being less progressive than her constituency could withstand. But of the more conservative Democrats, she’s the one who also has a rival politician eager to gamble on a primary challenge to an incumbent.

This logic reminds me of Dave Barry's explanation of the decision to nuke Japan in World War II:

It was Truman who made the difficult decision to drop the first atomic bomb on the Japanese city of Hiroshima, the rationale being that only such a devastating, horrendous display of destructive power would convince Japan that it had to surrender. Truman also made the decision to drop the second atomic bomb on Nagasaki, the rationale being that, hey, we had another bomb.

Yglesias's only criteria for evaluating the suitability of a primary challenge are whether there's a challenger and whether there's potential support for a challenger. There's no room in his calculus for determining whether a challenge is appropriate. Hey, we had a candidate.

My argument is that many Democratic members of Congress don't deserve to be challenged in primaries, and that Lincoln is one of them. Yglesias concedes that Lincoln is "far from the worst offender in terms of being less progressive than her constituency could withstand." That's an understatement! She's far more progressive than her constituency could withstand. So much more progressive that's she's almost certain to lose (90%, according to 538's model.) Is the idea that she should be taking even more risks for the same of the progressive agenda? Maybe push it up to 95% chance of losing?

I could see an argument for deploying challengers wherever you can find them just to throw the fear of God into Democrats in Congress. Perhaps the fact that Lincoln is almost certain to lose makes her an especially good target. There was a scene in "The Untouchables" where a federal agent, played by Sean Connery, is trying unsuccessfully to get one of Al Capone's hireling to talk. So he goes outside the room, picks up the corpse of one of the bad guys, starts interrogating him as if he's still alive, and then shoots him. The bad guy inside the room, unaware that the colleague that Connery shot was already dead, immediately becomes terrified and starts blabbing. See the first minute of this:

If you're not following my analogy, the progressives are Sean Connery and the corpse is Blanche Lincoln. If you're going to make an example out of somebody, why not pick somebody who's already (politically) dead? Or so the logic might go.

Still, I think you really want to make examples out of members of Congress who less liberal than they need to be to win, not members who are more liberal.