The invaluable Nate Silver is being very uncharacteristically obtuse. Yesterday, I reacted to Arlen Specter's decision thusly:

When a politician switches parties, it’s customary for the party he’s abandoned to denounce him as an unprincipled hack, and the party he’s joined to praise him as a brave convert who’s genuinely seen the light. But I think it’s pretty clear that Specter is an unprincipled hack. 

Nate writes:

One criticism of Arlen Specter I don't quite get, at least coming from liberals, is that his party switch reflects poorly on his character. Glenn Greenwald and Jon Chait, who don't actually agree on all that much, respectively call him "soul-less", and an "unprincipled hack".
Of course this is true, in so far as it goes.  ... But if you're a Democrat, would you really want Arlen Specter to be anything other than a soulless, unprincipled hack?

Yes, it's definitely good for the Democrats that Specter is such an unprincipled hack. That was my premise. I was saying that Democrats might be tempted to overlooking Specter's hackery because it benefits them, but we should be honest about what's really going on here. I think Nate is assuming that my assessment of Specter merely reflects the strategic interests of the Democratic Party, but the spirit of my post was actually just the opposite.

--Jonathan Chait