Ben Smith notes that in 1994, seven Congressional Democrats went over to the GOP, suggesting that Specter's switch to the Dems "could be the beginning, not the end, of a party shuffle." The obvious candidates to follow Specter--since I don't think Richard Burr or John Cornyn is going to become a Dem any time soon--are his fellow Northeastern Republicans, Maine Senators Susan Collins and Olympia Snowe. But I doubt this is going to happen. Unlike Specter, they don't face a mortal threat from their own state GOP, if only because Collins isn't up for reelection until 2016 2014 and Snowe isn't up until 2012. Yes, Snowe is offering up negative quotes about the GOP in the wake of Specter's switch, but she was offering up similar quotes nine years ago when Jim Jeffords left the GOP.

So, for that matter, was Specter. From a 2001 NYT article on Jeffords's switch:

Senator Arlen Specter, a Pennsylvania Republican who frequently votes with the moderates, said the loss of Mr. Jeffords was ''like a death in the family,'' and it had prompted a lot of soul-searching. ''I do believe that there will be some changes in the Republican caucus to reflect the more centrist positions,'' he said. ''We really have to face up to the fact that we lost some key seats in the last election.''

Of course, Specter didn't find it in his soul to bolt the GOP until he realized he was going to lose his reelection campaign. I think it'll take a similar realization for Snowe and Collins to do the same.

--Jason Zengerle