President Barack Obama added his name on Monday to the list of political heavyweights coming out in droves to stump for Democratic Rep. Joe Sestak in his battle for Pennsylvania’s open Senate seat.

Obama headlined a fundraiser for Sestak in Philadelphia at 5:10 p.m., which was to be followed by remarks at a dinner reception at 6:05 p.m. The events mark Obama’s first campaign visit for Sestak.

The Democratic Congressman has been leaning heavily on star power in his effort to defeat the GOP challenger, former Rep. Pat Toomey. Vice President Joseph Biden and President Bill Clinton both went to Philadelphia to lend support to Sestak last week.

Toomey was at least 9 percentage points ahead of Sestak in three of four recent public polls, a standing that has captured the attention of Democratic Party leaders determined to keep the seat currently held by Sen. Arlen Specter, whom Sestak defeated in the primary in May. The Democratic Senatorial Campaign Committee has set aside $5.7 million for the race, more than double the $2.5 million being spent by the National Republican Senatorial Committee.

Obama’s decision to campaign for Sestak marks a turning point in their relationship. Before Sestak became the Democratic nominee, the White House asked Clinton to persuade Sestak to abandon the primary race by raising the possibility of an unpaid administration position — an offer Sestak refused.

Specter, who was among those who greeted Obama on the tarmac when he landed in Philadelphia on Monday, dodged questions about the state of Sestak’s campaign when approached by a pool reporter.

Asked how he thought Sestak was doing, Specter paused for a few seconds before responding, “I’m late for the squash court, so I’m going to defer that to when I can answer in one spot.”

Pressed on whether his response should be taken as a sign that Sestak’s campaign did not appear to be going well, Specter again paused before responding, “Ah, I’m late for the squash court.”