Clinton bounded out of his black SUV in front of the building, bear-hugged Sestak and then grabbed Sestak's 5-year-old daughter, Alex, who is recovering from brain cancer.
"Hello, Beautiful," Clinton said.
The former president told Sestak how proud he was of him and then, unexpectedly, walked with the Sestaks back to the party and schmoozed with the 800 or so Pennsylvanians who had traveled to Washington to celebrate.
Earlier, Clinton accompanied his wife, Sen. Hillary Rodham Clinton (D., N.Y.), to her ceremonial swearing-in.
Holding the hand of his daughter, Chelsea, he led the family down the corridor to the Old Senate Chamber for the reenactment of the ceremony that had taken place earlier on the Senate floor.
The large security detail and a fusillade of flashbulbs upset what had been a relatively orderly procession.
The former president made one unscheduled stop - to the men's room in the press gallery.
Striding into the room, as reporters watched C-Span or dozed on the leather couches, he was gracious.
"They said this men's room was the closest," said the former leader of the free world. "Thanks for letting me stop by."
Sightings on Capitol Hill: Former senator and astronaut John Glenn of Ohio; singer Tony Bennett, a friend of newly anointed House Speaker Nancy Pelosi (D., Calif), making sure her heart remained in San Francisco; former New Jersey Gov. Jim Florio; and former Sen. Chuck Robb of Virginia, who with his wife, Lynda Johnson Robb, accompanied new Sen. Jim Webb (D., Va.) to his swearing-in.
Sen. Bob Casey Jr. (D., Pa.) was accompanied to the ceremony by his wife, Terese, their four daughters, and his mother.
Herding his clan into the Old Senate Chamber for the ceremonial reenactment with Vice President Cheney, Casey clutched a 30-year-old family Bible that had been inscribed and given to his father, the late former Pennsylvania governor, at a state constitutional convention.
"We've had a couple of family swearing-ins with this," Casey said with a smile.
But the second time around was just for the photographers. As Casey faced Cheney, ready to repeat the oath, the vice president smiled and made small talk.
"It's a reenactment," he said. "You don't have to say the oath again. You're already on the payroll."
For the record, the former Pennsylvania state treasurer had been between jobs and unemployed for one day.
Being a Democrat had its privileges yesterday, but new Rep. Patrick Murphy of Bucks County found that being a new father didn't carry much weight.
Murphy and his family arrived at the Rayburn Room in the Capitol for the ceremonial picture-taking with Pelosi, only to discover the kind of line seen only at Disneyland and in the former Soviet Union.
Clutching his 6-week-old daughter, Maggie, with his wife, Jenny, looking on anxiously, Murphy was prepared to wait after one of the gatekeepers said, "We have a lot of children here."
Finally, someone - maybe a former airline employee - took pity on the Murphys and allowed them a kind of "pre-boarding" near the front of the queue.
After the reenactment, Murphy, an Iraq war veteran, said he felt overcome by emotion thinking about his Army buddies still involved in the conflict.
"It's a very similar oath to what you take as a commissioned officer in the Army," Murphy said. "I started thinking about my friends still in Baghdad now. We have to have a change in direction in what's going on in Iraq."
Contact staff writer Steve Goldstein at 202-408-2758 or email@example.com.