Support for President Biden’s reelection bid seems to be dropping by the day, as a new survey suggests that the overwhelming majority of Americans believe Mr. Biden is not mentally or physically fit enough to serve as commander-in-chief, and nearly a majority of Democrats say his campaign should be ended. 

According to a CBS News–YouGov poll released Sunday, Mr. Biden’s debate performance on Thursday night has the vast majority of voters concerned about his well-being. When asked if he has the “mental and cognitive” abilities to serve as president, just 27 percent said Mr. Biden has that fortitude, compared to 50 percent who said the same about Trump. Nearly three-quarters of voters say Mr. Biden does not have the constitution to be sitting behind the Resolute Desk. 

In total, 72 percent say Mr. Biden’s “should not be running” for president this year. When asked their reasons for why they think the president should abandon his campaign, 86 percent say it is his age and physical and mental abilities. 

The debate helped contribute to the dramatic swing against Mr. Biden, according to the poll. Nearly 80 percent of poll respondents say they either watched all or part of the debate live or saw important highlights, and those who did see parts of the 90-minute debacle say Trump won overwhelmingly. Just 16 percent say Mr. Biden came away the victor, compared to 56 percent who said Trump won and 28 percent who said it was a tie. 

In one of the more devastating takeaways from the poll, even Democratic voters apparently want their own party standard-bearer to step aside for a different candidate. Just 54 percent of Mr. Biden’s fellow Democrats want him to stay in the race, compared to an astonishing 46 percent who say he should drop out. Among those Democrats who say he should step down, 95 percent say his age is their greatest concern. 

Because of the debate, the general election has become more salient earlier than ever before. Nearly two months before Mr. Biden is due to even be officially nominated as the Democratic candidate, 87 percent of Americans say they are at least paying some attention to the race. 

The CBS News–YouGov poll was conducted on Friday and Saturday immediately following the debate and included the opinions of more than 1,100 voters. 

Democratic Party leadership seems to care little about their own voters’ concerns, however. Within 24 hours of the debate, Presidents Obama and Clinton had already circled the wagons, brushing off Mr. Biden’s weak night as nothing more than one bad debate. 

“Bad debate nights happen. Trust me, I know. But this election is still a choice between someone who has fought for ordinary folks his entire life and someone who only cares about himself,” Mr. Obama wrote on X. Mr. Clinton said he would “leave the debate rating to the pundits.”

In the media, reaction to the Biden debate may have been even more swift than the recoil of Democratic Party voters themselves. By the end of the day on Friday, the editorial boards of the New York Times, the Chicago Tribune, and Atlanta Journal Constitution, among others, had called on the president to step aside for someone else. The editor of the New Yorker, David Remnick, said Mr. Biden’s decision to soldier on with his fledgling campaign “would be an act not only of self-delusion but of national endangerment.”

Republicans in Congress are already saying that Mr. Biden should not only end his campaign for the country’s and his own good, but he should step aside immediately and allow Vice President Harris to take over. On Friday, Congressman Chip Roy introduced a resolution that would call on the vice president to gather signatures of cabinet members to invoke the 25th Amendment in order to take over as Acting President. 

Ms. Harris’ office said she would do no such thing. 

Mr. Biden and his family are spending time together at Camp David in Maryland on Sunday with few staff and no national attention. It follows a number of meetings among Biden campaign staff and members of the Democratic National Committee about the fallout from the debate, though party leaders have reportedly been telling supporters and other prominent Democrats to do nothing more than stay the course with their current nominee.