Mark Hemingway offers what I assume will be a typical piece of conservative humor, quipping: “I read that he was switching parties, but I was disappointed to learn he’s still a Democrat.”
Joking aside, a look at the DW-NOMINATE scores shows that in the 110th Senate Specter was exactly what he claimed to be—a Republican who was less conservative than many other Republicans. Maine’s Olympia Snowe was to the right of all the Democrats, but to the left of all the other Republicans. Then Susan Collins was one click to her right. Then there was Gordon Smith and Norm Coleman and then Specter. In the 109 you didn’t have Smith and Coleman trying as desperately to position themselves as moderate for re-election purposes, so it went Chafee, Snowe, Collins, Specter. In the 108 it was Chafee, Snowe, Collins, Specter.
Thus, even if Specter were to reposition himself as the most conservative member of the Democratic Party he’d still have to become more left-wing than he’s been. What’s more, in the past there’s been a tendency for party switchers to suffer from ideological drift. Jim Jeffords went from being more conservative than most Democrats to being solidly liberal, and Ben Nighthorse Campbell went from being more liberal than most Republicans to being virulently right-wing.