Joe Biden 'must reconsider' re-election bid: Barack Obama

In a major development, former United States president Barack Obama has reportedly told allies that Joe Biden must reconsider whether to stay in the White House race, as the US president remained holed up at his beach house Thursday with about of Covid.

The former president believed the 81-year-old Biden, his vice president for eight years, should "seriously consider the viability of his candidacy," the Washington Post reported.

Biden's candidacy is on a knife-edge with a growing list of senior Democrats calling on him to step aside as concerns about his age and health spark fears that he is on course to lose badly to Donald Trump in November.

While rival Trump prepares for his star turn at the Republican National Convention in Milwaukee later Thursday, Biden finds himself in both personal and political isolation.

His personal doctor, Kevin O'Connor, said Thursday that Biden was still experiencing mild Covid symptoms and was taking the drug Paxlovid, but that his vital signs remain normal.

"He will continue to conduct the business of the American people," O'Connor said in a letter released by the White House.

His Covid diagnosis came at the worst possible time for his campaign, forcing him to cut short a trip to Las Vegas and isolate at his holiday home in Rehoboth Beach, Delaware.

Biden told reporters on Wednesday that he was "doing well" but was later seen looking frail as he slowly descended the steps of Air Force One.

Calls for Biden to step aside have grown since a disastrous debate performance against Republican Trump three weeks ago in which he appeared tired and confused.

A drumbeat of US media reports has suggested that the clock is ticking on his bid to prevent Trump making a sensational White House comeback.

The top Democrats in Congress, Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries, both reportedly met with Biden in recent days to warn that his candidacy threatens his party's prospects in November's election.

'Close to the end'

Influential former House speaker Nancy Pelosi added to his woes by privately telling Biden he cannot win and could harm Democrats' chances of recapturing the lower chamber, CNN and the New York Times reported.

The Axios news outlet quoted party figures as saying that Biden could drop out as soon as this weekend, while broadcaster NBC quoted a person close to Biden as saying: "We're close to the end."

Biden's campaign however insisted that he was staying in the race.

"Our campaign is not working through any scenarios where President Biden is not the top of the ticket," deputy campaign chairman Quentin Fulks told a press conference on the sidelines of the Republican convention in Milwaukee.

White House National Security spokesman John Kirby meanwhile said Biden was being "kept up to speed" by his team despite the political turmoil and his illness.

However the split-screen with Donald Trump could not be more stark, with Trump set to formally accept the Republican nomination in Milwaukee as Biden hunkers down.

Former president Trump, who at 78 is just three years younger than Biden, is riding a wave of support from his party after surviving an assassination attempt on Saturday that left him with a bandaged ear.

The United States could now be approaching the climax of an extraordinary period of political drama.

Any move to replace Biden on the ballot, with Vice President Kamala Harris leading the contenders, would likely come ahead of the Democratic National Convention starting in Chicago on August 19.

Biden has said she "could be president" but would not step down unless hard polling data or a medical condition persuaded him he could not beat Trump in November.