As Biden has experienced a wave of support in the party, amid public mourning over the death of his son Beau and Hillary Clinton's sagging poll numbers, many Democratic senators say that he'll soon experience the true taste of a political campaign once he decides to throw his hat in the ring.
The discussions have begun to occur in the private corridors of the Capitol. Late last month at a Democratic lunch, Sen. Claire McCaskill of Missouri privately noted that Biden-the-candidate will be treated far differently than Biden-the-lame-duck-vice-president, according to two attendees who asked not be named because such meetings are supposed to be off the record. His long record will come into focus, she said, including his questioning of Anita Hill during Clarence Thomas confirmation hearings.
McCaskill, in an interview, denied that she criticized the vice president. But she said that she often speaks about the political realities of a rigorous presidential campaign.
"There's a difference between potentially being a candidate -- and being a candidate," McCaskill said Tuesday. "And once you step onto the playing field, then everybody who runs is criticized, and everybody is looking for a way to win. It's just different when you're in the battle and when you are thinking about being in the battle."
That sentiment runs deep in the Senate Democratic Caucus. Even though one of their own, Sen. Bernie Sanders of Vermont, an independent who caucuses with the Democrats, is running an insurgent campaign and Biden, who served in the Senate for 36 years, is contemplating a run, most of the 46 members of the Democratic Caucus either publicly or privately back Clinton.
"It's a pretty cruel world out there once you're an announced candidate," said Senate Minority Whip Dick Durbin of Illinois, when asked about Biden. "I think there's a lot more scrutiny and a lot more criticism when you're an announced candidate."
Democratic senators have been watching Clinton's slide in the polls with increased anxiety, worried she has failed to put the controversy over her private email server behind her, giving rise to a potential candidate to knock her from the nomination. There is a widespread view within the caucus that a strong Clinton candidacy could be enough to propel Democrats back to the Senate majority, especially with key battleground states like New Hampshire, Florida, Ohio and Pennsylvania at play in 2016.
But a weakened Clinton has fallen behind Sanders in New Hampshire -- and she could see her lead elsewhere drop substantially if Biden gets into the race. A CNN/ORC poll from September showed that Clinton's lead grew nationally by 15 points without Biden in the race.
What makes the matter even more difficult for Senate Democrats is many consider Biden to be a close, personal friend, forcing them to choose sides in an increasingly contentious intraparty war.
While Virginia Sen. Tim Kaine said, "I love the vice president" and that his entry wouldn't be "catastrophic" to Clinton, he added: "My hope is that he doesn't get in."
Kaine added: "There's a difference between goodwill, and 'We really care about you as a person and really respect you' versus 'We want to pick you for this job.' There's just a difference. He knows that very well."
Indeed, Biden, 72, is well aware of the challenges of a presidential run, something he has been discussing with his team of friends and advisers over the last several weeks.
Delaware Sen. Chris Coons, a rare Biden supporter in the Senate who occupies the seat the vice president used to hold, said a "more vigorous campaign will strengthen whoever our nominee ultimately is."
Some Democratic supporters of Clinton agree.
"I think the more the merrier in the primary," said Sen. Gary Peters, D-Michigan. But Peters added that assuming Biden gets into the contest, things will change. "It simply is a different dynamic. It's one thing when you are being courted by folks. And it's another thing when you are running and on the campaign trail. "
For that reason, some Biden friends are worried that a campaign will only badly damage his legacy.
"I think the world of him," said Sen. Joe Manchin, D-West Virginia, who backs Clinton. "This man has endured an awful lot in his life. And he has the admiration and praise of the whole country."
But Manchin added that if Biden doesn't get in, "he will go out on top."