US President Joe Biden has begun to accept the idea that he may not be able to win the 5 November election and may have to drop out of the race, the New York Times has reported, citing several people close to the president.
Earlier, it emerged that former US president Barack Obama reportedly told allies in recent days that Mr Biden's path to victory in the US election has greatly diminished.
Mr Obama thinks Mr Biden needs to seriously consider the viability of his candidacy, the Washington Post has reported, citing multiple people briefed on Mr Obama's thinking.
It said there was no immediate comment from Mr Obama, who was in office while Mr Biden was vice president from 2009 to 2017 and who remains hugely influential in the Democratic Party.
Mr Obama would be the most heavyweight Democrat so far to join a growing chorus in the party calling for Mr Biden to drop out, following a disastrous debate performance against Donald Trump.
Mr Biden, who is isolating with Covid-19 at his beach house, has rejected concerns about his age and fitness and insisted that he is staying in the race for the White House.
Pressure is mounting, though, with Democratic Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries also both reportedly meeting with Mr Biden in recent days to warn that his candidacy threatens his party's prospects in November's election.
Last night, Mr Biden tested positive for Covid-19 while on a campaign trip to Las Vegas and has experienced mild symptoms, according to the White House.
"I feel good," Mr Biden said, giving reporters the thumbs up as he leaned out of his limousine dubbed "The Beast," before boarding Air Force One to head for isolation at his home in Delaware.
The announcement came minutes after the head of a Latino union said Mr Biden had called to apologise that he could no longer address its members because he had been diagnosed.
"Earlier today following his first event in Las Vegas, President Biden tested positive for Covid-19," spokeswoman Karine Jean-Pierre said in a statement.
"He is vaccinated and boosted and he is experiencing mild symptoms. He will be returning to Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time."
Mr Biden's doctor was suffering from a runny nose and a "non-productive cough" along with "general malaise," the White House said in an accompanying note.
He is now receiving the Covid drug Paxlovid, it added.
"His symptoms remain mild, his respiratory rate is normal at 16, his temperature is normal at 97.8 and his pulse oximetry is normal at 97%".
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President of the Unidos union Janet Murguia told the crowd about the diagnosis shortly before the White House announcement.
"I was just on the phone with President Biden, and he shared his deep disappointment at not being able to join us this afternoon," she said.
"The president has been at many events, as we all know, and he just tested positive for Covid.
"So of course, we understand that he needs to take the precautions that have been recommended."
Biden may drop election bid if 'medical condition' arises
Separately, Mr Biden has said that he might rethink his election bid if a "medical condition" emerged, according to an extract of an interview, as his health faces scrutiny after a disastrous debate.
"If I had some medical condition that emerged, if somebody, if the doctors came and said 'you've got this problem, that problem,'" Mr Biden told the media outlet BET in the sit-down interview taped earlier today, when asked what could make him rethink.
Mr Biden has faced fresh criticism as a heavyweight Democrat urged him to abandon his reelection bid and a backlash grew over plans for a virtual nomination before the party conference.
White House officials meanwhile believe former House of Representatives Speaker Nancy Pelosi backed California Representative Adam Schiff's call for Mr Biden to step aside in the race.
Ms Pelosi has told Mr Biden he cannot win the 5 November election, a top White House source with direct knowledge of the matter said.
Mr Schiff urged Mr Biden to "pass the torch", becoming one of the highest profile Democrats to do so and the first since the assassination attempt against Donald Trump.
"A second Trump presidency will undermine the very foundation of our democracy, and I have serious concerns about whether the president can defeat Donald Trump in November," Mr Schiff said in a statement to the Los Angeles Times.
"Nancy is all over this. She doesn't miss. Schiff wouldn't move without her approval," said the source, who spoke on condition of anonymity.
Ms Pelosi is "convinced public sentiment is against POTUS (president of the United States) and he can't change it," the source added.
Mr Schiff, who is expected to win a Senate seat this November, is a key White House ally in the legislature and came to nationwide prominence as lead prosecutor during then-president Mr Trump's first impeachment trial.
The chorus of Democrats calling for Mr Biden to step aside was briefly stopped by the attempt on Republican rival Mr Trump's life on Saturday, but has now started up again.
Around 20 House Democrats and one senator have now called on Mr Biden to leave the White House race but Mr Biden has refused, insisting he is best placed to beat Mr Trump.
Most polls show Mr Biden trailing in a tight race, with Mr Trump pulling ahead in key swing states but no dramatic movement since the debate debacle or shooting.
'Pretty damn good', Biden tells NBC
Mr Biden said his mental acuity was "pretty damn good" in an NBC interview yesterday, one of a series of unscripted outings in recent weeks aimed at showing he has what it takes.
He has blamed the debate on illness and jetlag, while his campaign says a series of recent verbal flubs are par for the course for a man famous for gaffes during a political career lasting more than four decades.
With pressure on Mr Biden mounting, Democrats said they plan to hold a virtual nomination for the president in the first week of August, ahead of the Democratic National Convention on 19 August.
Some Democrats have criticised the scheme, accusing the party of trying to fast-track Mr Biden's candidacy and avoid a full discussion of alternative choices.
Vice President Kamala Harris is considered the frontrunner if Mr Biden does drop out, although he has shown no sign he will.
Party chiefs say they need to carry out the virtual rollcall by 7 August, which is the deadline set by Republican-led state of Ohio for the submission of nominations.
Mr Biden otherwise risks not being on the ballot in Ohio, the home state of Mr Trump's new running mate JD Vance.
While Ohio's governor has signed a law giving Mr Biden more time, the DNC said it feared further legal challenges.
The DNC's rules committee said in a letter to politicians obtained by AFP that "no virtual voting will begin before 1 August," adding that it aimed to make a final decision next week.
"None of this will be rushed," it said.
"No matter what may be reported, our goal is not to fast-track," it added.
But several politicians are planning to sign a letter against the virtual nomination plan and others have criticised it, according to US media.
Mr Biden insists that Democratic voters support him, but a poll by the Associated Press and NORC Center for Public Affairs Research said that nearly two-thirds want him to step aside.
