Senator Bernie Sanders, a prominent figure of the US political left, has voiced support for Joe Biden's presidential candidacy despite calls for him to withdraw over health concerns.
"Enough! Mr. Biden may not be the ideal candidate, but he will be the candidate and should be the candidate," the independent senator wrote in a New York Times column, adding that "it's time for Democrats to stop the bickering and nit-picking."
Mr Sanders' column comes amid steadily growing calls from Democratic officials and donors for the 81-year-old Mr Biden to step aside following a disastrous performance in his 27 June debate with former president Donald Trump.
So far, some 20 members of Congress have called for him to leave the race.
Most polls taken since the debate show Mr Trump, who is 78, with a national lead over Mr Biden, though within the margin of error. They also show some key battleground states shifting in the Republican's direction.
The Vermont senator noted in his op-ed that he had strong disagreements with Mr Biden on some issues.
Mr Sanders, who is 82, has a strong following among young Americans, and like many of them he opposes what he called "US support for Israel's horrific war against the Palestinian people."
Mr Sanders also acknowledged the signs of the president's aging.
But given Mr Biden's accomplishments - and the record of Trump, "who has 34 felony convictions and... has told thousands of documented lies" - the senator brushed Mr Biden's shortcomings aside.
"Yes, I know," he wrote. "Mr Biden is old, is prone to gaffes, walks stiffly and had a disastrous debate with Mr Trump. But this I also know: A presidential election is not an entertainment contest. It does not begin or end with a 90-minute debate."
Mr Biden, he said, was "a good and decent Democratic president with a record of real accomplishment" who holds "the most difficult and stressful job in the world."
"For the sake of our kids and future generations, he must win."
Biden tells Detroit rally 'I am running and we are going to win'
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Mr Biden held a rare rally in Detroit, telling a cheering crowd he was not going to leave the race and warning that Mr Trump poses a serious threat.
"I am running and we're going to win," he said to a crowd that carried "Motown is Joe town" signs and chanted "Don't you quit" before he spoke.
"I'm the nominee," he said. "I'm not going anywhere."
"It's time for us to stop treating politics like it's entertainment or a reality TV show," the President added.
He warned that "Project 2025," a conservative policy platform that would seek to slash the federal government if Mr Trump is elected, was "deadly serious."
Earlier, Mr Biden made a surprise stop at a garage-themed restaurant in a western suburb of Detroit, where he told diners he planned to "finish the job," and said "I promise you...I'm okay."
As Air Force One flew to Motor City, campaign spokesperson Michael Tyler told reporters that donations "exploded" during Mr Biden's Thursday night press conference to seven times the usual level.
Mr Biden also got a boost earlier in the day when two prominent Democrats - Representative James Clyburn and California Governor Gavin Newsom - said he should stay in the race.
Yesterday, United Auto Workers president Shawn Fain, who had previously said he was worried about Mr Biden's chances, praised the President for standing "with the working class," without using his name.
However, there were signs that his support was weakening elsewhere, as two more politicians 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. Mr Levin, like many others who have called on Mr Biden to drop out, faces a competitive re-election battle of his own this year.
Since the debate, at least 19 politicians have urged Mr Biden to step aside so the party can pick another candidate, as have some donors, Hollywood stars, activist groups and news outlets.
Mr Biden retains support from key figures in the party, however, and has vowed to contest the 5 November election.
"I'm riding with Biden no matter which direction he goes," Mr Clyburn said on NBC's Today programme. Mr Newsom likewise said he was sticking with Mr Biden in an interview excerpt released by CBS.
Mr Clyburn, 83, is a respected voice among black Americans whose support is essential to Mr Biden's 2024 campaign, while Mr Newsom, 56, is one of several younger governors who are widely seen as the future of the party.
While Mr Biden courted Michigan voters, Mr Trump challenged him 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."
Mr Trump will be in the national spotlight next week, when the Republican Party holds its convention in Milwaukee to award him the presidential nomination.
Democrats are worried that Mr 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 Mr Trump win the White House.
As he worked to stem further defections, Mr Biden held separate phone calls with groups of Hispanic, Asian and Democratic politicians, according to aides. While the Hispanic group's top two leaders have endorsed Mr Biden, some other members have not stated their positions.
Democratic office holders, donors and activists are trying to determine whether Mr Biden is their best bet to defeat Mr 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.
Hakeem Jeffries, the Democratic leader in the House, said he met with Biden to convey the range of thoughts his 213-member caucus held about Mr Biden's candidacy. He did not say whether he personally thought Mr Biden should stay in the race.
"I directly expressed the full breadth of insight, heartfelt perspectives and conclusions about the path forward," Mr Jeffries wrote in a letter to colleagues.
Thursday's closely watched press conference provided fodder for Mr Biden supporters and doubters alike.
At one point, Mr Biden referred to his vice president, Kamala Harris, as "Vice President Trump." Hours earlier he introduced Ukrainian President Volodymyr Zelensky 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 found Mr Biden leading Mr Trump 50% to 48%, a slight increase from his position before the 27 June debate.
However, some analysts have warned that Mr Biden is losing ground in the handful of competitive states that will determine the outcome of the election.
Additionally, two dozen former congressional Democrats published an open letter Friday urging President Biden to allow other candidates to compete for the party's presidential nomination ahead of November's US election.
In the letter, the 24 signees said Mr Biden would "best serve the nation he loves" by releasing delegates who are pledged to vote for him at the Democratic National Convention - which is otherwise set to cement his role as the party's official nominee - and instead allow others to compete to lead the ticket.
"We are confident that one or more capable Democratic candidates would step forward. Excitement and optimism would ensue," read the letter addressed to the "American people" and reported by Politico.
Nineteen of the Democratic party's currently serving politicians have called on him to bow out of the race due to concerns over his health and mental acuity in the wake of the 27 June debate debacle.
"The President's integrity and vision are intact. However, the energy and stamina the President needs for a campaign and a next term are diminished," the letter said.
It added that it was concerned not just about the presidency but also congressional seats sliding into Republican hands.
"If the worst happens and we face another Trump term, the Democrats need at least one house of Congress to protect our liberty and the rule of law from total GOP control of the federal government," the letter said.
