Arlen Specter certainly would have lost a Republican primary for his Senate seat. But will he win a Democratic primary? That question turns, presumably, on who runs against him and, at least as importantly, on the posture of the party establisment in Pennsylvania and nationally.
It seems likely that Specter sought assurances on the Democrats’ posture towards his candidacy before making his switch, and that he made the switch only after obtaining some. It also seems likely that, before giving Specter assurances, the Democratic establishment would have extracted some promises from him.
The most important promise Specter could have given was not to stand in the way of passing the so-called Employee Free Choice Act, which would enable unions to represent a bargaining unit through a “card check” without winning an election. Specter has said he opposes this legislation and that his shift across the aisle will not change this. But the Democrats don’t need Specter to support card checks; they only need him to support cloture (i.e. to vote to cut off the filibuster).
To my knowledge, Specter has never said how he would vote on cloture in this context and thus remains a “free agent” on this precise issue. So perhaps he has now assured Democrats that he will support cloture, which possibly could clear the way for passage of “card checks.”
If Specter were to vote against cloture on this legislation, it seems clear that organized labor would try to take him down in the Democratic primary. And given labor’s strength among Pennsylvania Democrats, it is possible that, quite apart from any commitments Specter may already have made, he will think twice before he becomes the vote that kills the Employee Free Choice Act.