For some time, Senate Democrats knew there was an issue with their aging colleague, but they hesitated to publicly criticize or question someone they considered one of their own.
This person was a legend in the party, after all, someone with a storied legacy who had earned the right to remain and who had made it clear they weren’t going anywhere, ever — at least not voluntarily.
Besides, many senators were not much younger themselves, and nudging aside someone whose age was showing would prompt uncomfortable self-reflection. Even when the issues reached a point where they were too obvious for anyone to ignore, no party leader in Congress — including Senator Chuck Schumer of New York, the majority leader — wanted to be the first to start a public campaign to push out a friend and ally.
The dilemma Democratic senators are now facing regarding what to do about President Biden’s teetering presidential campaign is a familiar one for members of the aging chamber, who have watched many of their colleagues — including Mr. Biden, who served in the Senate for three decades — hold onto positions of power as they grow older.
They most recently lived through a similarly awkward and painful situation with former Senator Dianne Feinstein of California in the final years of her life.
Her condition was much more clear-cut than Mr. Biden’s; as it advanced, Ms. Feinstein began using a wheelchair and, by all accounts, was clearly in the later stages of dementia, unable to carry out daily tasks on her own. Mr. Biden’s precise health status is not known and he appears able to perform many elements of his job, though his disastrous debate performance called attention to what people around him described as more frequent lapses that raise questions about his mental acuity, his physical strength and whether he is up to the high-stakes task of defeating former President Donald J. Trump.
But the dynamic that has so far helped to keep Mr. Schumer and his Democratic colleagues from publicly calling on Mr. Biden to withdraw from the presidential race is similar to the one that surrounded Ms. Feinstein’s case.
It is fueled by the factors that have helped create the country’s geriatric political class, including an unwillingness to question incumbency and accumulated power; inner circles of staff that are personally and politically invested in protecting their aging bosses; and a sense of loyalty and legacy that often trumps pragmatism.
In this extreme case, however, all of that is tempered by a fear among Democrats that failing to replace Mr. Biden could cost them the White House and both chambers of Congress. Some Democratic staff members in both chambers expect the dam to break on Tuesday, when members of the House and the Senate both hold their weekly closed-door party meetings and lawmakers have an opportunity to conspire in person and will have to answer questions from reporters.
But they also said they never underestimate members’ ability to get cold feet.
For now at least, many Democratic senators appear to be hoping that members of the more rambunctious House — five of whom have already publicly called on Mr. Biden to exit the race — will be the ones to generate the pressure that will lead the president to withdraw.
“They don’t like to do that; it’s extremely rare,” Chris Whipple, a White House historian who wrote a book about the Biden presidency, said of senators publicly pushing out a colleague or party leader. “As of now, they’re going to Biden with an argument that, ‘We don’t think you’re up to it,’ and he says, ‘I know I’m up to it — and what’s more, all of these Democrats voted for me.’ He has a stronger hand than they do.”
Mr. Biden aggressively played that hand on Monday, effectively calling the bluff of Democrats in Congress who have quietly urged him to end his candidacy with a letter in which he said he was “firmly committed to staying in the race.”
“If any of these guys don’t think I should run, run against me,” Mr. Biden said not long afterward when he called in to MSNBC’s “Morning Joe” on Monday. “Go ahead, announce for president. Challenge me at the convention.”
It was reminiscent of Ms. Feinstein’s defiance in the face of questions about whether she should stay in the Senate. Ms. Feinstein refused to engage in any conversations about stepping down before the end of her term, despite being dogged by serious questions about whether she was fit to continue representing the 40 million residents of her state.
“I continue to work and get results for California,” she said at the time.
And just as Mr. Biden is now doing, Ms. Feinstein dared her fellow Democrats with concerns to publicly come at her and call for her to step aside.
They never did.
Mr. Schumer publicly stood by her decision to stay on.
Representative Nancy Pelosi of California, the former speaker, aggressively dismissed the calls for Ms. Feinstein to resign as sexist and argued that her legacy as a pioneering woman in politics had earned her the right to stay in office as long as the voters continued putting her there.
When Ms. Feinstein’s long-term absence from the Senate last year affected the business of the Judiciary Committee, Senator Richard J. Durbin, Democrat of Illinois and the chairman of the panel, went on television to deliver what was hardly a stern message to his ailing colleague. Mr. Durbin said he hoped she made “a decision soon as to whether she’s coming back.”
Some Democratic senators have begun to openly suggest that Mr. Biden needs to at least consider standing aside.
On Monday, Senator Jon Tester, a vulnerable Democrat from Montana who is up for re-election, said Mr. Biden “has got to prove to the American people — including me — that he’s up to the job for another four years.”
Senators Christopher S. Murphy of Connecticut and Michael Bennet of Colorado made similar noises over the weekend, as did Senator Angus King of Maine, an independent who caucuses with Democrats.
Senator Peter Welch of Vermont has warned of a “fierce undertow” for Democratic House and Senate candidates if the party’s presidential candidate loses badly in November.
Democrats have also spent months telling voters that the very future of democracy is on the ballot in November.
Still, in the 11 days since Mr. Biden’s disastrous debate performance, Senate Democrats have appeared to be consulting the same handbook they used last year with Ms. Feinstein. They have stayed mostly silent, even as they privately fret that the president’s feeble candidacy could cost them not only the White House, but control of the Senate and their chance to gain control of a House that has been dysfunctional under Republican control.
Mr. Whipple said the only thing that could change Mr. Biden’s defiant stance would be if the top Democrats in Congress, joined by his closest political confidants in both chambers, staged an intervention. If “a private delegation consisting of Chuck Schumer, Hakeem Jeffries, but probably also Jim Clyburn and Chris Coons, could somehow magically assemble,” Mr. Whipple said, “maybe he would listen.”
As of Monday, none had materialized and instead more Democrats were publicly declaring their allegiance to a president who has made it clear he will not be easily pushed aside.
Senator Catherine Cortez Masto, Democrat of Nevada, issued a statement on Monday saying that the president had “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.”