Of seven high-profile Democrats endorsed by Obama, Specter is the fourth to lose in the last seven months

WASHINGTON -- The role of endorser in chief isn't working so well for President Barack Obama.

Sen. Arlen Specter, a five-term incumbent who switched from Republican to Democrat last year in hopes of keeping his Pennsylvania seat, 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, closely divided between Democrats and Republicans, 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.

Still, Obama's poor record thus far could hurt his legislative agenda if Democratic lawmakers decide they need some distance from him as they seek re-election in what is shaping up as a pro-Republican year. Conversely, it might embolden Republican lawmakers and candidates who oppose him.

Obama's track record also raises the question of whether he may be hurting candidates he supports by motivating his foes -- such as tea party supporters -- to vote. Though this month's AP-GfK Poll shows Americans split about evenly over how he's handling his job, those strongly disapproving outnumber people who strongly back him by 33 percent to 22 percent -- not an enviable position for the president's party.

Sestak's victory over Specter is especially embarrassing, because he won by portraying himself and his supporters as being more faithful to the Democratic Party than were Specter and his backers -- who included the president, Pennsylvania Gov. Ed Rendell and other high-ranking party officials.

Creating another bruise for Obama and the Democratic establishment Tuesday, Sen. Blanche Lincoln was forced into a runoff in Arkansas' Democratic senatorial primary. Obama supports her bid for a third term, but he is not as closely associated with her campaign as he was with Specter's.

In previous months, Obama's endorsements and campaign appearances weren't enough to save then-Gov. Jon Corzine's re-election bid in New Jersey, Creigh Deeds' run for governor in Virginia or Martha Coakley's campaign in Massachusetts to keep the late Edward M. Kennedy's Senate seat in Democratic hands.