Nate Silver proves scientifically that the only thing Arlen Specter stands for is re-election. Bonus: he appears to have made Pat Toomey actually competitive in the general race, which certainly wouldn't be true normally.
This may give pause to those who are advocating that the Democrats "discipline" the Blue Dogs. Many of them are in districts that lean Republican much more firmly than Pennsylvania has swayed left. A primary challenge from the left would be a sad joke.