JONATHAN MARTIN | Hillary Clinton Debate Performance Chills Biden Movement

Screen Shot 2015-10-14 at 8.15.21 PMOCT. 14, 2015

LAS VEGAS — Democrats expressed growing skepticism on Wednesday that Vice President Joseph R. Biden Jr. could find a foothold were he to enter the presidential campaign as Hillary Rodham Clinton’s commanding performance in the first Democratic debate here abruptly quieted murmurs about her candidacy.

With no obvious constituency ready to support Mr. Biden, his prospects have increasingly been based on the possibilities of Mrs. Clinton’s faltering, repeating some of the missteps she has made since declaring her candidacy earlier this year or falling prey to more damning revelations about her use of a private email server as secretary of state.

But with Mrs. Clinton showing her mettle in Tuesday’s debate, and Democrats increasingly convinced that questions about her emails are little more than a Republican and news media fixation, she suddenly appeared far better positioned to allay skeptics in her party when she testifies next week before the congressional panel investigating the attacks on the American consulate in Benghazi, Libya.

Screen Shot 2015-10-14 at 8.08.58 PMBiden ‘Proud’ of Debate Candidates

As he pondered his own White House bid, Vice President Joseph R. Biden Jr. said Wednesday he thought the Democratic hopefuls did well.

By THE ASSOCIATED PRESS on Publish DateOctober 14, 2015. Photo by Doug Mills/The New York Times. Watch in Times Video »

“If Biden’s only rationale is that Clinton is tanking, then that’s no longer an option,” said Stephanie Cutter, a longtime Democratic consultant. Mrs. Cutter, who worked for President Obama’s re-election, said Mr. Biden could now “risk a backlash” from Democrats if he runs.

With crisp answers to nearly every question, an aggressiveness her rivals did not seem ready for and a level of confidence that has often been obscured over months of email questions, Mrs. Clinton sent an unmistakable message to Mr. Biden and to her party.

By Wednesday, Democrats unaffiliated with any candidate were describing the closing, if not the slamming shut, of a door.

“The dilemma Vice President Biden faces about the 2016 race today underscores the fact that successful campaigns aren’t based upon the expected failures of your opponent,” said Mary Anne Marsh, a veteran Democratic strategist.

No less a critic of Mrs. Clinton than Donald J. Trump, the Republican contender, conceded on MSNBC’s “Morning Joe” that Mrs. Clinton “did what she had to do.”

Mr. Biden, of course, may not be dissuaded from giving up what could be his last chance at the presidency. “I’m not sure that’s entirely what’s going to drive Joe’s decision,” Ed Rendell, the former Pennsylvania governor and Clinton supporter, said on MSNBC of Mrs. Clinton’s showing in the debate.

Screen Shot 2015-10-14 at 8.12.44 PMMr. Biden, briefly speaking to reporters Wednesday, shed no new light on his deliberations but said he had felt “proud” watching the night before. “I thought every one of those folks last night — I’m mildly prejudiced — I thought they all did well,” he said.

Mrs. Clinton’s backers here were elated, suggesting that her authoritative performance offered an unspoken rejoinder to those Democrats calling for Mr. Biden to make a late entry into the race. “I think that kind of cemented it,” said Representative Dina Titus, Democrat of Nevada. “She said, ‘I’m a progressive who can get things done.’ That’s the perfect combination that we need.”

Mrs. Clinton’s articulation of her brand of mainstream liberalism was also an implicit statement to Mr. Biden that there is no more space in the Democratic contest for somebody who would also carry the banner of the center-left and run as Mr. Obama’s heir. Again and again, it was Mrs. Clinton who portrayed herself as Mr. Obama’s partner, the candidate who would perpetuate and enhance the president’s legacy.

She did not exactly issue a call for four more years, but while Senator Bernie Sanders was calling for a political revolution, Mrs. Clinton, more than any other candidate, embraced Mr. Obama and his politics.

Mr. Sanders offered her a crucial assist on two fronts in forestalling a threat from Mr. Biden.

Mr. Sanders’s unsteady response to her surprisingly tough attacks on guns — the one issue on which she is safely able to outflank him from the left — gave Mrs. Clinton an opportunity to solidify her support among the nonwhite Democrats Mr. Biden would need to defeat her. Polls show that some of the strongest supporters of gun control are African-Americans and Hispanics.

And by effectively offering her a political amnesty on her email travails — saying “the American people are sick and tired of hearing about your damn emails” — Mr. Sanders made it difficult for himself to seize on the issue should it worsen, and gave Mrs. Clinton a way to isolate Mr. Biden should he try to use the subject to attack her character.

But what may have been the most lasting result of the first Democratic face-off was Mrs. Clinton’s attempt to fend off a threat from the vice president by linking herself so closely to the president they both served. “The Obama heir with her own credentials and opinions,” as Ms. Cutter put it.

Mrs. Clinton turned to Mr. Obama as a shield when faced with questions that could raise doubts about her on the left.

“Well, I recall very well being on a debate stage, I think, about 25 times with then-Senator Obama, debating this very issue,” Mrs. Clinton said when the first hint of criticism arose about her initial support of the Iraq war. “After the election, he asked me to become secretary of state. He valued my judgment, and I spent a lot of time with him in the Situation Room, going over some very difficult issues.”

Asked about her differences with the president, she first sought to avoid the question entirely, then said only that she would “build on the successes” of Mr. Obama and attempt to go even further in some policy areas. She called him “a great moral leader” on racial issues and defended his decision to use American forces in Libya.

Mrs. Clinton never mentioned Mr. Biden — his name did not come up once during the entire debate — but she alluded to one of the most memorable areas on which she and Mr. Obama were in agreement, but the vice president was not. Recalling the “tough decision that President Obama had to make about Osama bin Laden,” Mrs. Clinton noted that she was “one of his few advisers” on that question — seeming to catch herself so as not to point out that Mr. Biden had had doubts about that military operation.

It was a walk-to-the-edge caution that her advisers and surrogate supporters also employed after the debate, when they were clearly instructed to follow Mrs. Clinton’s respectful line on all questions about the vice president’s plans.

But even as they offered the usual acknowledgments of the personal decision Mr. Biden has to make, there was also just a touch of bravado in the wake of Mrs. Clinton’s strong showing.

“We’ve come to the point where he should decide,” said John Podesta, Mrs. Clinton’s campaign chairman. “And if he’s going to get in, we’re going to run our race. And I think you saw that race being run tonight. She just hit it out of the park.”