Nearly two-thirds of Democrats say President Joe Biden should withdraw from the presidential race and let his party nominate a different candidate, according to a new poll, sharply undercutting his post-debate claim that “average Democrats” are still with him even if some “big names” are turning on him.

The AP-NORC Center for Public Affairs Research poll found 65% of Democrats and 70% of Americans want Biden, 81, to step down. 

Nearly half of Democrats (48%) now lack confidence that he has the mental capability to serve effectively as president, up from 32% in an AP-NORC poll in February.

Biden, 81, in an interview excerpt with BET released Wednesday made the stunning concession that if a medical professional gave him an unfavorable evaluation he would reconsider his candidacy.

“If I had some medical condition that emerged, if somebody, if doctors came to me and said, you got this problem and that problem,” Biden said in an excerpt released Wednesday.

At the same time, Democrats’ dissatisfaction with Biden as their nominee has surged 16 percentage points in the last month, with a June 20-24 poll showing 39% expressing disease with him at the top of the 2024 ticket and a July 11-15 poll revealing that number rising to 48%.

Biden delivered a disastrous debate performance against former President Donald Trump on June 27, followed by several weeks of scattered remarks in public press conferences and stumbling media interviews — leading to more calls from Democrats for him to abandon his 2024 run.

As of Wednesday, 21 Democratic members of Congress — including most recently Rep. Adam Schiff (D-Calif.), who is running for an open Senate seat in November — had called for Biden to drop out.

The AP-NORC poll was conducted mostly before Saturday’s assassination attempt on Trump at a campaign rally in Pennsylvania.

The shooting, which killed one and wounded two other rallygoers, slowed the “momentum” of a potential Biden ouster, a Democratic operative told The Post Sunday, but by two days later had regained momentum.

But when asked in the AP-NORC survey, respondents did not give any of Biden’s potential successors high marks.

Only 30% said Vice President Kamala Harris would make a good president, 17% said California Gov. Gavin Newsom would and 15% said Michigan Gov. Gretchen Whitmer would — despite each being discussed as replacement candidates.

“I do have genuine concerns about his ability to hold the office,” Democratic voter Andrew Holcomb, 27, of Denver told the Associated Press. “I think he’s frankly just too old for the job.”

Janie Stapleton, a 50-year-old lifelong Democrat from Walls, Mississippi, held the opposite view, saying Biden is the “best candidate” for president.

“I just feel like these two individuals are a sad choice,” added Alexi Mitchell, 35, a civil servant who lives in Virginia. She identifies as a Democratic-leaning independent, and while she thinks Biden is probably still mentally up to the job, she worries that the past few weeks’ unraveling of support makes him a weak candidate, no matter what happens next. “If he doesn’t have control over his own party, that’s a fatal flaw,” she said. “He’s put us in a bad position where Trump might win.”

David Parrott, a Democrat from Soddy-Daisy, Tennessee, was also willing to give Biden the benefit of the doubt given the president’s age, but he still voiced concerns about a potential second term.

“I don’t know if he can make it another four years or not,” said Parrott, a 58-year-old retiree. “Shouldn’t he be sitting at his beach house taking it easy?”

Americans remain much more likely to think Trump is capable of winning the 2024 election than is Biden — 42% to 18% — with nearly a quarter saying the candidates have an equal chance of beating the other.

Trump also has the edge on Biden when Americans consider who is most capable of handling a crisis, 38% to 28%.

And people are about equally divided on which candidate has the better vision for the country, with 35% saying Biden and 34% Trump.

The poll, however, did offer a bright spot for Biden: 40% of adults say he’s more honest than Trump, while about 2 in 10 think the opposite.

The AP-NORC poll of 1,253 adults was conducted July 11-15 with a margin of sampling error for all respondents is plus or minus 3.8 percentage points.