Democratic anxiety over President Biden’s fitness to run for re-election erupted into the open on Tuesday in a spike of panic, as the first sitting member of Congress called on Mr. Biden to withdraw and a slew of other prominent officials who have backed the president vented their concerns.
One Democratic senator openly asked for assurances from the White House about Mr. Biden’s “condition” — “that this was a real anomaly and not just the way he is these days,” Senator Sheldon Whitehouse of Rhode Island told a local television station, where he said he had been “horrified” by the president’s debate performance.
Another, Senator Peter Welch of Vermont, scolded the Biden campaign for “a dismissive attitude towards people who are raising questions for discussion,” in an interview with Semafor.
And later on Tuesday, Representative Lloyd Doggett of Texas, a veteran progressive lawmaker, issued a statement saying that Mr. Biden’s debate performance, which he had hoped would give the president momentum to make up for his weakness relative to former President Donald J. Trump, had instead disqualified him from running again.
“I had hoped that the debate would provide some momentum to change that. It did not,” Mr. Doggett said. “Instead of reassuring voters, the president failed to effectively defend his many accomplishments and expose Trump’s many lies.”
The vast majority of Democrats, including party leaders, remain publicly supportive of Mr. Biden, and the few critics who have dared to voice their concerns so far are not major players in the party with large followings. Still, after days of privately fretting over Mr. Biden’s fumbling, faltering debate performance late last week, by Tuesday a growing number of Democrats appeared willing to air their frustrations.
It was a notable inflection point that came just a day after the president addressed the nation in prime time in an effort to assuage concerns about his ability to speak in public.
Distraught about the pressure from within Mr. Biden’s own firmament, White House officials were discussing sending Mr. Biden to battleground states, including to Wisconsin on Friday and Pennsylvania on Sunday, to do what allies have been urging: show him in public settings for longer durations. And they were discussing having Mr. Biden meet on Wednesday with Democratic governors, many of whom have not had direct contact with the president since the debate, causing exasperation among some who have yet to hear from him.
Much of the anxiety among lawmakers, strategists and operatives is being driven by a double-barreled fear — not just that Mr. Biden’s stumbles will cost him the White House, but that they might also make it impossible for Democrats to win the critical races that will decide control of the House and Senate, thus depriving them of a crucial check on the power of a potential Trump presidency.
“He clearly has to understand,” Representative Mike Quigley, Democrat of Illinois, said on CNN on Tuesday, “that his decision not only impacts who is going to serve in the White House the next four years, but who is going to serve in the Senate, who is going to serve in the House, and it’s going to have implications for decades to come.”
Many Democratic offices on Capitol Hill have reported being barraged by calls from their constituents urging lawmakers to ask Mr. Biden to step down. Mr. Doggett said in an interview that the calls and messages he was receiving from constituents and supporters were “10 to 1” in favor of Mr. Biden stepping down. Another recounted that the messages were divided evenly between constituents calling for Mr. Biden to withdraw and those who thought he was fit to serve.
And it is clear that Republicans plan to use the questions around Mr. Biden’s mental acuity and fitness for office as a millstone around the necks of vulnerable Democrats.
The day after the debate, Republican trackers — operatives who film candidates and pelt them with politically treacherous questions — followed frontline House Democrats on their way home to their districts and asked them the same question: “Is Joe Biden fit to be president?”
“Joe Biden is president,” Representative Marcy Kaptur, Democrat of Ohio, replied testily. “Are you fit to be president?”
But privately, many Democrats are deeply concerned. Democrats in congressional races across the country have long understood that they would need to outperform Mr. Biden in order to win their seats. In that sense, several party operatives working on congressional races said Mr. Biden’s performance would do little to affect their strategy.
Representative Jared Golden, Democrat of Maine, for example, who represents a district Mr. Trump won in 2020, said on Tuesday in an opinion column that he has long believed the former president would win in November — “and I’m OK with that.”
“Maine’s representatives will need to work with him when it benefits Mainers, hold him accountable when it does not and work independently across the aisle no matter what,” Mr. Golden wrote.
In a pair of statements from Democrats’ House and Senate campaign arms, spokesmen stressed that congressional races were “candidate vs. candidate battles,” as David Bergstein, the Senate campaign communications director, said.
But Mr. Biden’s debate performance, which unleashed a new wave of questions about his age and mental condition, has cast a dark shadow over the Democrats who are running down-ballot.
“It is noteworthy that our most significant Senate candidates have been running so significantly ahead of the president in places like Nevada and the rest of the country,” Mr. Doggett said in an interview. “But if we are not able to have a more vigorous and more effective campaign, we could end up with a Republican House and Senate. And there is concern that even if they have one of those houses, we have no check on Trump at all.”
Mr. Doggett said he believed that Democrats were in a good position to win control of the House. “But if you look at it state by state, the margin will be — under the best of circumstances — a modest one. And that is why we need all the help we can get from the top.”
For now, leading Democrats are expressing strong backing for Mr. Biden. Senator Chuck Schumer of New York, the majority leader, said during an appearance in Syracuse on Tuesday that, “yes,” he believed the president was fit to serve.
“I’m with Joe Biden,” he said.
Representative Nancy Pelosi, Democrat of California and the former speaker, said on Tuesday that it was “legitimate” to ask whether Mr. Biden’s bad night at the debate was a one-time flub or “a condition” — though she added that Mr. Trump should have to answer the same question about the falsehoods he uttered.
“I think it’s a legitimate question to say is this an episode or is this a condition,” Ms. Pelosi said in her first extended remarks since Mr. Biden’s halting and disjointed performance at the debate.
“When people ask that question, it’s legitimate — of both candidates,” she added. “What we saw on the other side was lying.”
(A spokesman later volunteered that Ms. Pelosi had “full confidence” in Mr. Biden and looked forward to attending his inauguration in January 2025.)
But for the first time, at least one prominent Democrat who remains behind Mr. Biden entertained questions about him withdrawing. Representative James E. Clyburn of South Carolina, whose support in 2020 helped Mr. Biden earn the Democratic nomination, said he would back Vice President Kamala Harris if the president stepped down.
“I will support her if he were to step aside,” Mr. Clyburn said on MSNBC on Tuesday, although he added: “I want this ticket to continue to be Biden-Harris.”
Top Democrats in informal conversations advised politically vulnerable candidates to respond however they felt was best for their individual race, whether that meant defending Mr. Biden or distancing themselves from him, according to people familiar with the discussions.
That has left many frontline Democrats faced with questions about Mr. Biden’s fitness trying to demonstrate independence to voters in their districts. One Democratic challenger, Adam Frisch in Colorado, who nearly ousted Representative Lauren Boebert in 2022, has called on Mr. Biden to step down.
“Panic is not a useful emotion, but neither is denial,” said John Avlon, a Democrat running against a Republican incumbent on Long Island. “President Biden had a bad debate, but he’s got a good record. This is a legitimate debate for Democrats to be having and it’s a sign of a healthy political party.”
It has placed Democrats running in battleground states including Wisconsin and Arizona, where Mr. Biden will campaign aggressively, in a particularly awkward position.
“I focus on my race; I’m not a pundit,” Senator Sherrod Brown, Democrat of Ohio, told reporters last week when asked about whether Mr. Biden should consider stepping aside.
Representative Matt Cartwright, the political veteran who represents Scranton, Pa., Mr. Biden’s hometown, is considered one of the most vulnerable House Democrats up for re-election this year. He told reporters at the Capitol the day after the debate that it would be a “big leap” for Mr. Biden to step aside.
But Mr. Cartwright must navigate the difficult political waters in his district, where an unpopular incumbent president might drag him down. He declined to be interviewed, but emphasized in a statement that he was his own man.
“The president had a tough night, but I’m running a different race in my community,” Mr. Cartwright said. “Northeastern Pennsylvania knows me. They know I’m delivering good-paying jobs, lowering prescription drug prices and sticking up for our rights.”
His opponent, Rob Bresnahan, was more than happy to try to tie his opponent to what he called a diminished president.
“He’s way past his prime, and it became obvious,” Mr. Bresnahan said about Mr. Biden in an interview. “Everyone saw this is our leader. This is our president. And Congressman Cartwright votes with this guy nearly 100 percent of the time. It’s the blind leading the blind.”
Some Democrats believe that if Mr. Biden stays in the race and continues to lag Mr. Trump in the polls or falls behind more, the party and its major donors may simply focus their money and energy on trying to keep hold of the Senate and win back the House rather than contest the presidency.
That was how Republicans handled the 1996 election with their presidential nominee, Bob Dole, trailing badly. Their efforts led the G.O.P. to maintain control of Congress, stymying the second term of Bill Clinton much as Democrats would hope to do during a second Trump administration.
“Democrats may say, ‘We’d better get our act together or we could lose everything,’” said Steve Jarding, a veteran Democratic political strategist and former lecturer at the Harvard Kennedy School. “And the American public seems to like divided government.”
Luke Broadwater, Maggie Haberman, Maya C. Miller and Aishvarya Kavi contributed reporting.