Since his son’s death, the vice president has spent most of his time with his family at home in Wilmington, Del., but he has made several forays to Washington in recent days wearing a simple black rosary with a religious medal on his wrist. Some who saw him at the White House said he seemed eager to get back into a work routine.

Some Democrats wonder whether Mr. Biden, 72, who served 36 years in the Senate and ran for president in 1988 and 2008, might emerge from the tragedy recommitted to public service and give another look at a third presidential bid. But several people close to Mr. Biden said they saw no real chance that he would run absent an unforeseen development taking Mrs. Clinton out of the race.

Still, unlike Senator Elizabeth Warren, the Massachusetts Democrat who consistently said she was not running despite a draft effort, Mr. Biden has not definitively said no, instead promising a decision by the end of summer. As long as he is not telling them to stop, the Democratic activists here in Chicago figure the door remains open.

Mr. Pierce said the committee got its start in his living room a few months ago when he sent out an email to 2,000 people arguing for a Biden presidential bid. He then went to the gym to work out.

“I came back and when I saw my email” there were “all these people who said, ‘We want to get involved,’” he said. “Since then, it’s just taken off.”