WASHINGTON (AP) — President Joe Biden stood firm Monday against calls for him to drop his reelection candidacy and called for an end to the intraparty drama that has torn apart Democrats since his dismal debate performance last month, as key lawmakers expressed support for him to remain in the 2024 presidential race.

As anxious congressional Democrats returned to Washington weighing whether to work to revive his campaign or to try to edge him out, Biden sent them an open letter aiming to silence their skepticism of his fitness to lead the country for another four years. He insisted he wasn't leaving the race and stressed that the party has "one job," which is to defeat presumptive Republican presidential nominee Donald Trump in November.

After a week of false starts, a coordinated effort by Biden and his campaign to shore up Democratic support appeared to be paying off, though he had by no means silenced his doubters. By late Monday, a sudden rush of public support from Democrats emerged — or at least some tempering of criticism — as Biden allies appeared to be trying to overpower the public and private voices calling on him to step aside.

Biden wrote in the two-page letter that "the question of how to move forward has been well-aired for over a week now. And it's time for it to end."

"We have 42 days to the Democratic Convention and 119 days to the general election," Biden said in the letter, distributed by his reelection campaign. "Any weakening of resolve or lack of clarity about the task ahead only helps Trump and hurts us. It's time to come together, move forward as a unified party, and defeat Donald Trump."

Biden followed up the letter with a phone interview with MSNBC's "Morning Joe" show, in which he insisted that "average Democrats" want him to stay in the race and said he was frustrated by the calls from party officials for him to step aside.

"They're big names, but I don't care what those big names think," Biden said.

He threw the gauntlet at his critics, saying if they're serious they ought to "announce for president, challenge me at the convention" or rally behind him against Trump. Later, Biden joined a call with members of his national finance committee, while first lady Jill Biden campaigned for her husband in a three-state swing focused on engaging veterans and military families.

"For all the talk out there about this race, Joe has made it clear that he's all in," she told a military crowd in Wilmington, North Carolina. "That's the decision that he's made, and just as he has always supported my career, I am all in, too."

Democratic voters are split on whether Biden should remain the Democratic Party's nominee for president, or whether there should be a different Democratic nominee, according to a New York Times/Siena College poll.

On Capitol Hill, more prominent voices lined up behind Biden, including the chair of the House's Congressional Progressive Caucus, Rep. Pramila Jayapal, who was not ready to cast aside the president, saying that the threat of a second Trump presidency remains too high. Yet one of the most endangered Democrats this election cycle, Sen. Jon Tester of Montana, said in a statement, "President Biden has got to prove to the American people — including me — that he's up to the job for another four years."

However, Biden's letter left some House Democrats, who want to hear directly from Biden himself, furious, according to one House aide granted anonymity to discuss the situation. Lawmakers particularly bristled at being cast as out of touch with voters since representatives in particular have been home in their districts listening to voters.

Biden met virtually Monday with the Congressional Black Caucus — one of his staunchest blocs of supporters in Congress — for 30 minutes. He told the group about his policy proposals for a second term, expressed gratitude to members for their support and repeatedly criticized Trump, according to a person familiar with the call and granted anonymity.

While not every member of the Black caucus spoke up, no one spoke out against the president, the person said.

Biden is also expected to meet this week with members of the Congressional Progressive Caucus, said Jayapal.

Meanwhile, press secretary Karine Jean-Pierre said Biden had undergone three neurological exams while in the White House as part of his annual physical exams — and no more — and said the president has not been diagnosed with or treated for Parkinson's.

The drama is playing out with just over a month until the Democratic National Convention and just a week before Republicans gather in Milwaukee to renominate Trump as their presidential pick.

Rep. Ayanna Pressley, D-Mass., part of a newer generation of progressive lawmakers, said she backed Biden and expressed worry that Democrats were taking their eye off defeating Trump. "We're losing the plot here," she said.

Another prominent voice in the Congressional Black Caucus, Rep. Maxine Waters of California, said those opposing Biden "can speak for themselves or what they want to do, but I know what I'm doing because I'm a big Biden supporter."

And Rep. Frank Pallone of New Jersey, the top Democrat on the Energy and Commerce Committee, said: "I'm tired of all this speculation. I just want to concentrate on the fact that we have to defeat Trump."

Trump, for his part, predicted that Biden would remain in the race. "It looks to me like he may very well stay in," he told Fox News Channel's Sean Hannity on Monday. "He's got an ego and he doesn't want to quit. He doesn't want to do that."

House Democratic leader Hakeem Jeffries, who has publicly stood by Biden even as he weighs how to address the concerns of many in his conference, said "same answer" Monday after an evening meeting the Capitol when asked if he supported Biden.

At the same time, other House Democrats almost ran from questions. Rep. Debbie Dingell, D-Mich., told reporters as she exited a leadership meeting that she was off to another meeting about the Great Lakes, and a group of House Democrats, including Reps. Abigail Spanberger of Virginia and Lauren Underwood of Illinois, changed the subject, declining to answer question as they ducked into an elevator.

Rep. Adam Smith of Washington, the top Democrat on the Armed Services Committee, went public Monday with his call for Biden to step aside, saying it would be "a mistake" if Biden continues his campaign. "I'm calling on President Biden to step down," Smith said on social media.

Biden's allies said they expected more direct engagement from the president with lawmakers — like the CBC virtual meeting — as he scrambles to shore up his candidacy. On a call Saturday with his campaign co-chairs, Biden repeatedly asked them who else needs to hear from him, who else he needs to engage with and who still has unanswered questions or concerns, according to Sen. Chris Coons, D-Del.

"He is out there doing his job as a candidate and doing his job as president," Coons said.

Rep. Annie Kuster of New Hampshire, the chair of the New Democrat Coalition, has asked House leadership to invite Biden to speak to the entire Democratic caucus.

If the president's going to stay in the race, "then help us respond to questions from our constituents," she said. "And it's so much easier to say, I was with him."

Rep. Nanette Barragan of California, the chair of the Congressional Hispanic Caucus, who supports Biden and campaigned recent with the first lady in Pennsylvania, said Biden "should talk to as many members as possible."

Senators returning to Washington Monday were generally reluctant to criticize Biden, and many said they were waiting for the Democratic caucus meeting on Tuesday to hear concerns. It was still unclear if any Senate Democrats would publicly call for Biden to go, even as many have expressed deep concerns in private conversations over the last 10 days.

"He ran an excellent campaign, and he's been an excellent president," said Colorado Sen. Michael Bennet. "And I think what everybody is trying to satisfy is that's the same trajectory and path that we're on today."

Senate Majority Leader Chuck Schumer would not answer questions about Biden's reelection as he entered the Capitol on Monday, but he told reporters, "As I've said before, I'm for Joe."

Another Democrat, Sen. Alex Padilla of California, said it was "time to quit the hand-wringing and get back to door knocking."

While some deep-pocketed donors may be showing discomfort, strategists working on House and Senate races said they have posted record fundraising as donors view congressional Democrats as a "firewall" and last line of defense against Trump.

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Associated Press writers Farnoush Amiri, Kevin Freking, Darlene Superville, Jill Colvin and Mary Clare Jalonick contributed to this report.