Sen. Arlen Specter became the fourth Democrat in seven months to lose a high-profile race despite the president's active involvement, raising doubts about Obama's ability to help fellow Democrats in this November's elections.

The first three candidates fell to Republicans. But Specter's loss Tuesday to Rep. Joe Sestak in Pennsylvania's Democratic senatorial primary cast doubts on Obama's influence and popularity even within his own party — and in a battleground state, no less.

Of course, it's possible that Democrats will fare better than expected this fall. And there's only so much that any president can do to help other candidates, especially in a non-presidential election year. ...