After a rough summer, Hillary Clinton's advantages in experience and composure were clear when she shared a stage with her rivals for the first time, says The Post's Dana Milbank. (Tom LeGro/The Washington Post)

LAS VEGAS — The possibility of a late entry by Vice President Biden into the 2016 sweepstakes has been premised at least in part on Hillary Rodham Clinton's weaknesses as a possible Democratic nominee.

But after Clinton turned in a sterling debate performance here Tuesday night, rebounding from what had been a terrible summer on the campaign trail, Democratic officials were abuzz about the implications for Biden, who has spent the past several months weighing a bid and is poised to announce a decision later this month.

In the spin room following the debate, Clinton's allies as well as senior Democrats who have not taken sides in the primary said a debate that is likely to give Clinton a needed jolt of momentum also may have sucked a lot of air out of the Biden balloon. How, they wondered, could Biden now convince donors and other top Democrats now backing Clinton to abandon her and join his campaign?

Former Los Angeles mayor Antonio Villaraigosa, a Clinton supporter who attended the Las Vegas debate as a surrogate for her, all but said Biden could not.

“Neither Hillary nor I want to weigh in on the vice president’s decision-making here," Villaraigosa said. "This is a decision he’s making with his family. But if you’re asking me, 'Did she look unbeatable tonight,' the answer is, 'yes.' Is she the candidate the Republicans fear the most? The answer is, 'yes.' Did she look presidential, calm, deliberate, passionate about the issues? The answer is, resoundingly, 'yes.'"

The official line from the Clinton campaign was that they were thrilled with the candidate's performance and that Biden had to make his own decision.

John Podesta, the Clinton campaign chairman who worked closely with Biden in President Obama's White House, made clear how difficult a campaign against a resurgent Clinton would be.

“He needs to make up his mind," Podesta said of Biden. "She put in a tremendous debate performance tonight and I think that she occupied a space in the party that showed that she was going to fight for this nomination, take the fight to the Republicans, put forward a program that people could really grab onto, believe in, and she was going to fight for the people she’s been fighting for all her life. If he wants to get in and challenge her, then he needs to do that, and that’s his right.”

Asked whether Clinton's debate performance closes the door for Biden, Joel Benenson, Clinton's top strategist and pollster, would not give an assessment.

“This debate was about the five people on this stage who are in this race," Benenson said. "The vice president is entitled and deserves time to make this decision on his own terms and on his own basis, and that’s all I’m going to say on that.”

Randi Weingarten, president of the American Federation of Teachers, which has endorsed Clinton, was asked whether the debate impacted Biden's political viability. She said "he has to make the decision for himself," but added, "I think what you saw here tonight is that there is a clear standard-bearer for Democratic values and for the Democratic Party."

That was a view echoed Tuesday night throughout the Democratic establishment. Henry Muñoz III, who as the national finance chairman of the Democratic National Committee must stay neutral in the nominating contest, chose his words carefully.

“I think that many people continue to wait for the vice president to make a decision. I’m one of them," Muñoz said. "But if he decided not to run, I feel very confident that one of the people standing on the stage is capable of running the country.”