So my earlier prediction that Arlen Specter would become a Democratic stalwart in the Senate has not fared so well. First, he voted against the budget (I wrote that off to his already established opposition to that spending plan as it would have seemed too opportunistic to switch on that!) Then he reasserted his opposition to Obama's health care proposals and card-check unionization. And then he dropped the bomb: saying the Minnesota courts should "do justice" and seat Norm Coleman (Specter says he forgot what team he was on -- switch parties after 29 years and it slips your mind!)
Of course, my prediction about the repercussions if he didn't become a Democrat's Democrat was correct. The Democratic caucus, under considerable pressure from liberal interest groups, voted not to recognize his seniority (at least until after such point as he was elected as a Democrat). This makes it increasingly likely that Specter will face a primary challenge from Joe Sestak who will be well funded by the liberal groups who despise Specter for his work on the Judiciary committee over the years.
Even if Specter had moved further to the left, it is not that unusual for the receiving party to be somewhat inhospitable to a switcher. Many of the southern Democrats who switched parties as that region went Republican were challenged or defeated in primaries by purer conservatives. As the Northeast goes Democratic, Republican switchers probably shouldn't expect much better treatment. Of course, the Democrats are taking a bit of a gamble that Sestak can beat Toomey head-to-head.