As Joe Biden took to the stage for a rally in Detroit, Michigan, on Friday evening, one of the most raucous crowds seen in recent years at any event for the US president chanted: "Don't you quit!"

The presumptive Democratic nominee was greeted by deafening cheers from hundreds of supporters as he vowed: "I am running! And I'm gonna win!"

As he left the stage, the strains of Tom Petty's hit I Won't Back Down washed over the high school gymnasium, an implicit rebuff to the growing list of elected members of his party exhorting him to step aside amid concerns about his age.

But for all the headlines dominated by the latest politician, donor or liberal actor to turn on Mr Biden, a longer list of Democrats are sticking by him.

At least 80 Democratic politicians have publicly backed the 81-year-old, and more are joining them as he insists he is going nowhere.

To many, his political record, his principles and his 2020 victory over Donald Trump mean more than the damage of a rambling performance in any debate or public appearance, or health fears during a new four-year term.

In Mr Biden's first solo news conference of the year on Thursday, he gave detailed responses on Nato and his plans for a second term, but many headlines focused on his flub in referring to his deputy, Kamala Harris, as "Vice-President Trump".

His allies - for now, at least - praised the embattled commander-in-chief's performance, which was watched live by over 23 million people - a bigger audience than this year’s Oscars.

"I thought he showed a real command of foreign policy, really extraordinary," North Carolina Governor Roy Cooper told reporters on Friday. "I don’t think Donald Trump can talk about foreign policy coherently for one minute."

Gavin Newsom, the California governor touted as a possible successor, told CBS he was "all in" for Mr Biden, adding that there was "no daylight" between them.

Congressman Brendan Boyle of Pennsylvania said Mr Biden "showed he knows a million times more about policy" than Trump, "the convict conman".

Experts say these politicians have a host of reasons for their support, including Mr Biden's record in office, his 2020 victory against Trump and the gamble of putting in a new candidate so close to the November election.

"The president has made it clear he wants to continue to run, and I think people are being very respectful of that," said Simon Rosenberg, a Democratic strategist.

"And it's also true that in our system, replacing a candidate for president this late is hard and is unprecedented, and so there's enormous reticence about making a big change."

He added that there was a "healthy debate" about who the nominee should be.

However, a range of groups have said that the candidate should be Mr Biden, including the Congressional Hispanic Caucus, which has about 40 members, and the 60-member Congressional Black Caucus, which Mr Biden met earlier this week.

Ameshia Cross, a former Obama campaign adviser, said that the black caucus, as well as many black voters, see Mr Biden as a president committed to civil rights, unlike his rival, Trump.

"They understand what is at stake with a Donald J Trump presidency," she said. "This is a guy who has stood against DEI - diversity, equity and inclusion efforts."

Mr Biden has received public support from several politicians on the left, including the New York congresswoman Alexandria Ocasio-Cortez and Senator Bernie Sanders of Vermont, who have previously criticised Mr Biden for an agenda they have said is too moderate.

Ms Cross said many recognise the risks a Trump presidency brings to civil and LGBTQ rights and climate change.

"These are things that matter to the progressive left, and the president has actually worked on those things," she said.

To date, most of Mr Biden's support comes from politicians running for re-election in reliably Democratic districts, rather than those who worry Mr Biden could harm their own election chances in tougher seats.

Mr Rosenberg said that the White House "needs to be respectful of their concerns and deal with them, I think, in a far more aggressive manner".

Even as calls grow for Mr Biden to exit the race, the most recent poll seems to suggest that he has not lost much voter support.

The Biden campaign has touted a survey from the Washington Post, ABC News and Ipsos published this week, which shows him and Trump in a dead-heat, similar to survey results from before the debate. But the poll also found two-thirds of Americans want Mr Biden to step aside.

The president has also lost support from some among the Hollywood elite. Actress Ashley Judd called on Mr Biden to step down in a USA Today op-ed on Friday, saying the party needed a "robust" candidate. Her article followed an even more damning opinion piece this week by George Clooney about Mr Biden.

Longtime Democratic donor Whitney Tilson is the latest fundraiser to pull the plug, telling the BBC on Friday that he was increasingly confident Mr Biden would go. Other Democratic donors told a pro-Biden fundraising group, Future Forward, that pledges worth some $90m (£69m) were on hold until he exits, reports the New York Times.

Other top donors, however, are sticking by the president.

Shekar Narasimhan, who has been organising fundraisers for Democrats for more than two decades, said there had been no change in his plans.

"Our eyes can see what’s going on, our ears can hear what's being talked about but we are keeping our heads down to get the work done," said Mr Narsimhan, who is the founder of the Asian American Pacific Islander Victory Fund Super-PAC.

"It's the president’s decision to make, whether he wants to run or not, and we will go with whatever he decides," he said. "But it's better to end this discussion as soon as possible."

He said his support for Mr Biden came from the belief that he would win.

"This election will be decided by no more than a total of 50,000 votes in three states - Michigan, Pennsylvania and Wisconsin - and we have the ground game and infrastructure to win there," he said.

Frank Islam, who sits on the National Finance Committee, said he had a fundraiser planned at his Maryland home later this month. "I am absolutely going ahead with it because I know he [Mr Biden] will win," he said.