Remember when Arlen Specter switching parties was a sign of doom for Republicans?

Nine months later, it looks like one of the luckiest breaks for the GOP in 2009. Had he remained with the party, I suspect Pat Toomey would have beaten him in the primary, but that’s not a given. And lot of the GOP establishment would have gotten sucked into defending a wobbly vote in a primary fight that would have made the current Crist-Rubio tussle look like hug therapy. Now Toomey gets a smooth ride through the primary and can harness his resources for the general election.

Instead, the Democrats get to worry about whether Specter will survive the primary — that, too, looks iffy — and if he does, they get to spend millions to tell Pennsylvanians that the fossil who’s been there forever and who keeps snapping at people is their best possible choice to represent them for the next six years.