WASHINGTON (AP) — 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 new survey by the AP-NORC Center for Public Affairs Research, conducted as Biden works to salvage his candidacy two weeks after his debate flop, also found that only about 3 in 10 Democrats are extremely or very confident that he has the mental capability to serve effectively as president, down slightly from 40% in an AP-NORC poll in February.

The findings underscore the challenges the 81-year-old president faces as he tries to silence calls from within his own party to leave the race and tries to convince Democrats that he's the best candidate to defeat Donald Trump. The poll was conducted mostly before Saturday's assassination attempt on Trump at a campaign rally in Pennsylvania. It's unclear whether the shooting influenced people's views of Biden, but the small number of poll interviews completed after the shooting provided no early indication that his prospects improved.

Meanwhile, as Vice President Kamala Harris receives additional scrutiny amid the talk about whether Biden should bow out, the poll found that her favorability rating is similar to his — but the share of Americans who have an unfavorable opinion of her is slightly lower.

The poll provides some evidence that Black Democrats are among Biden's strongest supporters, with roughly half in the survey saying he should continue running, compared to about 3 in 10 white and Hispanic Democrats. Overall, seven in 10 Americans think Biden should drop out, with Democrats only slightly less likely than Republicans and independents to say that he should make way for a new nominee.

"I do have genuine concerns about his ability to hold the office," said Democrat Andrew Holcomb, 27, of Denver. "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.

People aren't just sour on Biden on as they size up their choices this election season.

About 6 in 10 Americans want Trump to withdraw -- but relatively few Republicans are in that camp.

As for Biden, younger Democrats are especially likely to want to see him bow out – and to say they're dissatisfied with him. Three-quarters of Democrats under the age of 45 want Biden to drop out, compared to about 6 in 10 of those who are older.

"I just feel like these two individuals are a sad choice," said 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."

Despite bullish talk from the Biden campaign heading into the debate, the faceoff only left the president in a deeper hole. Democrats are slightly more likely to say they're dissatisfied with Biden as their nominee now than they were before his halting performance. About half are dissatisfied, an uptick from about 4 in 10 in an AP-NORC poll from June.

By contrast, most Republicans – about 6 in 10 – came out of the debate very or somewhat satisfied with Trump as their candidate. Too few interviews were conducted after the assassination attempt to provide a clear indication of whether Republicans or Americans overall have rallied further around Trump since then.

David Parrott, a Democrat from Soddy-Daisy, Tennessee, was 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?"

All of the recent churn has left Americans much more likely to think Trump is capable of winning the 2024 election than is Biden – 42% to 18%. About a quarter thought the the two men equally capable of winning.

Even Democrats are relatively dour about their party's prospects come November.

Only about a third of Democrats believe Biden is more capable of winning than is Trump. About 3 in 10 think the two are equally capable of winning and 16% say victory is more likely to go to the Republican. By contrast, Republicans are overwhelmingly convinced that Trump is in the best position to win.

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.

For all of the disenchantment Biden is up against, the president insists it's not too late to turn things around, saying past presidents have come back from a deficit at this stage in the campaign. In an interview Tuesday with BET News, he said many voters haven't focused yet, adding, "The point is, we're just getting down to gametime right now."

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

Most Democrats — around 6 in 10 — say that Vice President Harris would make a good president, while 22% think not and 2 in 10 don't know enough to say. The poll showed that 43% of U.S. adults have a favorable opinion of her, while 48% have an unfavorable opinion. Somewhat more have a negative view of Biden: approximately 6 in 10 Americans.

The survey was conducted before Trump selected freshman Sen. JD Vance of Ohio as his running mate. It showed that for most Americans, Vance is still an unknown. Six in 10 don't know enough about him to form an opinion, while 17% have a favorable view and 22% view him negatively.

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The poll of 1,253 adults was conducted July 11-15, 2024, using a sample drawn from NORC's probability-based AmeriSpeak Panel, which is designed to be representative of the U.S. population. The margin of sampling error for all respondents is plus or minus 3.8 percentage points.