Well, why not? The Senate Democratic Caucus did everything but buy billboards in Pennsylvania to send a welcome message to Rep. Joe Sestak for a challenge to their newest, bestest Democratic buddy, the really junior Senator Arlen Specter (R D-PA).  As Brian Faughnan notes, Sestak seems to have his game plan well designed to run to Specter’s left:

Money quote:

I was just taken by a Washington DC political establishment — Democrat — that reached over to the Republican establishment for someone who had been there 50 years and said, “Pennsylvania, here’s your future.”  That’s not their decision.

No matter which side you’re on, that’s a great line, and one Sestak will use to great effect.  Well played, sir.

Here’s the problem for Democrats.  If Sestak gears up for a run at the Senate, his Congressional seat will likely go up for grabs, and Democrats only won that one back in 2006.  He may wind up damaging Specter but not beating him and giving up the seat to the GOP.  If he runs for both simultaneously in the primaries, he will have to hit Specter from the left while campaigning for re-election in his center-right Congressional district, which will also give the GOP some openings.  It puts both seats at risk, but apparently the Democratic caucus will chance it to get rid of Snarlin’ Arlen.