Via Benen, Arlen Specter is in serious trouble in the Democratic primary in Pennsylvania, with his lead over Joe Sestak down to four points (46/42) in the latest Rasmussen poll. Given that Specter enters with an enormous name recognition lead, I'd probably be inclined to put my money on the challenger in this one, although it's also true that PA Dems may not realize just how far Specter has zigged to the left since his big switch; he's voting like a mainstream Dem, not a marginal Dem. Obama is certainly popular among the PA Dem primary electorate, and he'll be doing plenty of education to drive home the best argument for Specter. Slight edge to Sestak at this point? OTOH, if anyone has great electoral survival skills, it's Arlen Specter.
At any rate, my real comment is that the showdown takes place in the spring. We know what happens if Specter wins the primary; he'll start floating back towards the middle.
But what if Specter loses? With electoral incentives gone, but with several months remaining in office, how will he vote? Will we find out who the real Arlen Specter is? (Does he even know at this point?). Will he find an industry to hitch his star to, in order to find a post-public service career there, and vote accordingly? Sure, he'll be 70 by then, but he doesn't really seem the type to just plain retire. Should Obama whisk him out of the Senate and into an ambassadorship ASAP, allowing a more-reliable placeholder to be appointed (if that's the law in PA; I don't know)? Is there a way for Obama and the Dems to legally signal that they'll take care of him with a post-election job (there's always a cabinet slot available if you need one for such purposes)?
Generally, the voting patterns of Members of Congress is reasonably predictable, even if specific votes can be a tough call. But a lame duck Arlen Specter, should PA Dems produce one? Absolute, total, wild card.