I'm generally of the opinion that it's great to have anyone as a Democrat who will caucus with the party and support its candidates. People get all bent out of shape about Ben Nelson (D-NE); and I'd count myself among the bent. But it'd be difficult to get a Democratic elected from Nebraska whose politics were dramatically different from Nelson's. And party's aren't political cells or even clubs; they/re coalitions.

This has mainly informed my opinion about Arlen Specter, given what I've always considered his relatively reasonable politics and what high-profile party switches almost always tell us about the shifting tectonic plates about the nation's politics. But Specter does seem to have been going out of his way, not just on the optics, which I can sort of understand (since he doesn't want to appear utterly craven), but also to oppose the consensus Democratic position on almost every issue. And in any case, Specter isn't just a Democrat in 2009 and 2010. He's running in the Democratic primary as a first time nominee for senate. And there's a decent argument to be made that the state could elect a substantially more progressive Democrat this year, though Pennsylvania Democrats, even ones that are pretty progressive on some issues, tend to be fairly conservative on others.

So it was with all that in mind that I read this typically meaty post from Nate Silver which notes that by some measures Joe Sestak, who's looking like Specter's most probable primary challenger, may actually be more conservative than Specter. (Note that SEIU head Andy Stern says he's holding a meeting with Sestak tomorrow.)

I guess my thought on this, to the extent it matters -- which isn't much since I'm not a Pennsylvania voter -- is that I'm happy to have him as a Dem. But it'd be nice to see him have to make some case to the Democrats in his state that he's worthy of their nomination -- something that could be accomplished either by Sestak threatening to get in or actually challenging him in the primary. Because at the moment at least it does seem like he's taking the matter entirely for granted.

Thoughts?