The vice president slipped into a booth at the Mayfair Diner next to a trio of middle-aged women.

"I don't mean to interrupt you," he said, grinning. "In fact, I did mean to interrupt you."

For the next half-hour, Biden worked the tables inside the narrow diner on Frankford Avenue with his trademark charm. He was on hand to campaign for U.S. Senate candidate Katie McGinty, who introduced herself to diners as "a good Northeast girl" with the accent to prove it. Sen. Robert P. Casey Jr. (D, Pa.) also attended.

"This is Katie McGinty," Biden said, turning to a pair of diners. "I hope you'll look her over, and if you don't, Bobby Casey and I are going to come to your house."

They slid into booth after booth to pose for pictures and shake hands. Conversation was light on policy and heavy on Northeast Philadelphia touchstones: Tastykakes and Catholic school educations and the city's hapless sports teams.

"You guys are tough fans," Biden said, commiserating with 92-year-old Margie Sonnie. She told him he was handsome. He showed her a rosary he carries with him - one that belonged to his late son, Beau.

The diner's owner, Manoli Lagoudakis, found out 15 minutes before Biden's arrival that the vice president was coming to his restaurant. He served Biden a cup of a coffee and a blueberry muffin.

"It was a pleasure," he said afterward.

This was Biden's second visit on McGinty's behalf, after touring a diner with her in Pittsburgh earlier this month.

The Democratic establishment - from President Obama and Biden on down to Gov. Wolf and key labor unions - has tried to rally McGinty to a primary victory over Democratic rival Joe Sestak, a retired admiral and former congressman from Delaware County.

Though trailing for most of the race, McGinty has surged into contention with help from millions of dollars in outside spending, and has prominently promoted her endorsement from Obama on television and radio.

Sestak, meanwhile, spent the weekend visiting black churches in Philadelphia, hoping to stir up support of his own. He says his backing comes from grassroots Democrats, not party power brokers.

The race is critical for Democrats nationally. They see unseating Sen. Pat Toomey (R., Pa.) as a key to taking back the Senate.