President Biden’s defiant call on Democrats in Congress on Monday to stop questioning his viability and fall in line behind his candidacy did little to quell the groundswell of skepticism within his own party that has engulfed his campaign.
As lawmakers returned to Washington after a weeklong recess, there were few signs that any of Mr. Biden’s efforts to reassure his allies — either through a bluntly worded letter or a phone interview on MSNBC — had done much to mollify growing Democratic anxieties.
Instead, ahead of a day of crucial meetings in which Democrats in the House and the Senate plan to meet separately to discuss a way forward, lawmakers were still openly agonizing over their presumptive nominee, with party divisions about the best course bursting into the open. And two more prominent Democrats came forward to air their concerns about Mr. Biden’s path to victory in November.
“With so much at stake in the upcoming election, now is the time for conversations about the strongest path forward,” Senator Mark Warner, Democrat of Virginia and the chairman of the Intelligence Committee, said in a statement. “As these conversations continue, I believe it is incumbent upon the president to more aggressively make his case to the American people, and to hear directly from a broader group of voices about how to best prevent Trump’s lawlessness from returning to the White House.”
Representative Adam Smith of Washington, the top Democrat on the Armed Services Committee, became the latest — and perhaps the most high profile — lawmaker to say publicly that Mr. Biden should step down, after first saying so in a private meeting of top House Democrats on Sunday.
“I think it’s become clear that he’s not the best person to carry the Democratic message,” Mr. Smith said on Monday in an interview on CNN, adding, “Personally, I think Kamala Harris would be a much better, stronger candidate.”
Mr. Biden began the day by firing off a missive that was aimed at tamping down any further calls for him to step aside and put an end to the hand-wringing on Capitol Hill.
“The question of how we move forward has been well aired for over a week now,” Mr. Biden wrote in his two-page letter to lawmakers. “And it’s time for it to end.”
But there was no end in sight on Capitol Hill, and only a few Democrats in Congress who unequivocally rallied to Mr. Biden’s side.
Senator Catherine Cortez Masto of Nevada, whose victory in 2022 tipped control of the Senate to Democrats, said in a statement that Mr. Biden “always had Nevadans’ backs, whether it’s on the picket lines, protecting our personal freedoms or lowering costs — now it’s time for us to have his.”
And Mr. Biden’s bloc of strong support from the Congressional Black Caucus grew, as its chairman, Representative Steven Horsford of Nevada, released a statement defending the president.
“President Biden is the nominee and has been selected by millions of voters across this country, including voters in Nevada,” he wrote in a social media post, adding that voters “know President Biden and Vice President Harris are fighting for them.”
Mr. Biden scheduled a virtual meeting on Monday evening with the Black Caucus, an influential group on Capitol Hill, moving to capitalize on the support and perhaps discourage others from breaking with a powerful piece of the Democratic coalition.
Senator Chris Coons of Delaware, a confidant of Mr. Biden’s and a co-chairman of his campaign, flatly declared: “President Biden will be the nominee for my party.”
The overall mood in Congress, though, was much more dour as lawmakers making their way back to Washington for the first time since Mr. Biden’s disastrous debate performance quietly fretted about his ability to defeat former President Donald J. Trump and the drag he might have on Democratic candidates running for House and Senate seats if he continued his campaign.
Many Democratic senators have long considered Mr. Biden, a creature of the Senate who served there for more than three decades, a personal friend and ally. But most have suggested that the onus is on the president to dispel any concerns among voters about his age and fitness.
Some appeared reluctant to say much on the matter before Tuesday, when Democratic senators plan to discuss Mr. Biden’s future at their weekly closed-door party luncheon. House Democrats are expected to have a similar discussion on Tuesday morning at their weekly party meeting. But those who did speak up made it clear they had major concerns about Mr. Biden continuing as the party’s candidate.
“I love Joe Biden,” Senator Martin Heinrich, Democrat of New Mexico, said in what has become a typical statement among his colleagues. “He’s the most accomplished president of my lifetime and he’s a genuinely wonderful human being. However, what I care most about is the preservation of our democracy.”
Mr. Heinrich, who is up for re-election this year, continued: “President Biden needs to continue to demonstrate that his debate performance was just a bad night, and that he has a clear path to defeating Donald Trump. Our democracy hangs in the balance.”
Senator Brian Schatz of Hawaii said in a terse statement that “the most important thing for Democrats or for the country is to beat Donald Trump,” and that Democrats needed to “have in-person family conversations about the best way to do that.” He declined to comment further.
Senator Michael Bennet of Colorado also would not commit to backing Mr. Biden as the party’s nominee, saying that Democrats needed to discuss the best way to win the White House and both chambers of Congress. “I want him to succeed,” Mr. Bennet said.
Jettisoning Mr. Biden, he continued, would be “no one’s first choice.”
“But we have a moral obligation to the country to establish that we can win the presidency, that we can win the House and that we can win the Senate,” he said. “We have to do that. We are here this week to have that conversation.”
Others offered terse endorsements. Senator Chuck Schumer of New York, the majority leader, has mostly repeated a clipped message of approval over the last week. “I’m with Joe,” he told reporters on Monday as he entered the Capitol. “I have no interest in walking away from him,” Senator Thomas R. Carper, Democrat of Delaware, told reporters outside his office.
And Senate Democrats running in the most politically treacherous races across the country, including Ohio and Montana, declined to provide any political cover for the president.
When Senator Sherrod Brown of Ohio was asked during a campaign stop about whether Mr. Biden should run for re-election, he replied, “I’m not a pundit.”
“I’ve talked to people across Ohio,” Mr. Brown said. “They have legitimate questions about whether the president should continue his campaign, and I’ll keep listening to people.”
And Senator Jon Tester of Montana issued a statement saying that Mr. Biden “has got to prove to the American people — including me — that’s he’s up to the job for another four years.”
Robert Jimison, Annie Karni and Maya C. Miller contributed reporting.