Seeking to revive his struggling reelection campaign, US President Joe Biden held a rare rally in Detroit on Friday, telling a cheering crowd he wasn’t going to leave the race and warning that Republican Donald Trump poses a serious threat.

Biden, 81, is trying to shift the conversation from his mental sharpness and a growing number of Democratic defections to the impact of another Trump presidency, as he tries to reboot his campaign after a shaky debate performance on June 27.

“I am running and we’re going to win,” he said to a crowd that carried “Motown is Joetown” signs and chanted: “Don’t you quit.”

“I’m the nominee,” he said. “I’m not going anywhere.”

Pointing to the press area in the gym, Biden said: “They’ve been hammering me,” to which the crowd booed. “Guess what, Donald Trump has gotten a free pass,” he added.

“Hopefully with age comes a little wisdom,” Biden said, in a defiant and sometimes gleeful performance.

“Here’s what I know — I know how to tell the truth, I know right from wrong … and I know Americans want a president, not a dictator.”

Biden also laid out what he intended to do with his first 100 days of a second term, including codifying abortion rights, signing the John Lewis Voting Rights Act, ending medical debt, raising the minimum wage and banning assault weapons.

These sweeping changes would be difficult or impossible without Democratic majorities in both houses of Congress.

While union and religious leaders attended, Michigan’s governor Gretchen Whitmer and its Democratic senators, Debbie Stabenow and Gary Peters, did not.

Earlier on Friday, Biden made a surprise stop at a restaurant in a Detroit suburb, where he told diners he planned to “finish the job,” and said: “I promise you … I’m okay.”

Biden got a boost on Friday when two prominent Democrats — Representative James Clyburn and California Governor Gavin Newsom — said he should stay in the race.

On Friday afternoon, United Auto Workers president Shawn Fain, who had previously said he was worried about the president’s chances, praised Biden for standing “with the working class”, without using his name.

But there were signs that his support was weakening elsewhere, as two more lawmakers called on him to drop out.

“It is time to move forward. With a new leader,” Representative Mike Levin, from California, said in a statement. Levin, like many others who have called on Biden to leave the race, faces a competitive reelection battle of his own this year.

Since the debate, at least 19 lawmakers have urged Biden to step aside so the party can pick another candidate, as have some donors, Hollywood stars, activist groups and news outlets.

Biden retains support from key figures in the party, however, less than five months from the November 5 election.

“I’m riding with Biden no matter which direction he goes,” Clyburn said on NBC’s “Today” programme. Newsom likewise said he was sticking with Biden in an interview excerpt released by CBS.

Clyburn, 83, is a respected voice among Black Americans whose support is essential to Biden’s 2024 campaign, while Newsom, 56, is one of several younger governors who are widely seen as the future of the party.

While Biden courted Michigan voters, Trump challenged him on Friday to take a cognitive test, writing on Truth Social: “I will go with him, and take one also. For the first time we’ll be a team, and do it for the good of the Country.”

Trump will be in the national spotlight next week when the Republican Party holds its convention in Milwaukee to award him the presidential nomination.

Crucial calls

Democrats are worried that Biden’s low approval ratings and growing concerns that he is too old for the job could cause them to lose seats in the House of Representatives and Senate, leaving them with no grip on power in Washington should Trump win the White House.

As he worked to stem further defections, Biden held separate phone calls with groups of Hispanic, Asian and Democratic lawmakers, according to aides. While the Hispanic group’s top two leaders have endorsed Biden, some other members have not stated their positions.

Democratic officeholders, donors and activists are trying to determine whether Biden is their best bet to defeat Trump and serve another four-year term in the White House.

The New York Times reported that unnamed donors have told a pro-Biden Super PAC fundraising committee that roughly $90 million in pledges will remain on hold as long as he is in the race.

As Air Force One flew to the Motor City, campaign spokesperson Michael Tyler told reporters that donations “exploded” during Biden’s Thursday night press conference to seven times the usual level.

Hakeem Jeffries, the Democratic leader in the House, said he met with Biden on Thursday night to convey the range of thoughts his 213-member caucus held about Biden’s candidacy. He did not say whether he personally thought Biden should stay in the race.

“I directly expressed the full breadth of insight, heartfelt perspectives and conclusions about the path forward,” Jeffries wrote in a letter to colleagues.

Thursday’s closely-watched press conference provided fodder for Biden supporters and doubters alike.

At one point, Biden referred to his vice president, Kamala Harris, as “Vice President Trump”.

Hours earlier he introduced Ukrainian President Volodymyr Zelenskiy as “President Putin” at the Nato summit, drawing gasps from those in the room.

He also delivered detailed assessments of global issues that served as a reminder of his decades of experience on the world stage.

With most US voters firmly divided into ideological camps, opinion polls show the race remains close.

An NPR/PBS poll released on Friday found Biden leading Trump 50 per cent to 48pc, a slight increase from his position before the June 27 debate.

But some analysts have warned that Biden is losing ground in the handful of competitive states that will determine the outcome of the election.

“If current trends continue, Mr Trump could rack up one of the most decisive presidential victories since 2008,” Democratic strategist Doug Sosnik wrote in the New York Times.