Joe Biden vows 'I'm staying in the race' amid speculation over his future

Joe Biden has again vowed "I am staying in the race" at a rally as pressure mounts on him to quit the presidential election.

Doubts grew over the health and capability of the 81-year-old US president after a shaky performance in a debate with opponent Donald Trump last week.

Amid questions about whether he has the stamina to run against Trump, he held a rally in the key battleground state of Wisconsin, ahead of an interview with broadcaster ABC News - his first since the debate.

Speaking to supporters, he said he is not letting the debate "wipe out years of work" and is "going to win again" in November.

"We had a little debate last week. Can't say it was my best performance. But ever since then there's been a lot of speculation," he said.

"What's Joe gonna do? Is he gonna stay in the race? Is he gonna drop out? Well here's my answer: I am running and gonna win again."

He also took aim at Trump's intelligence and called him a liar.

As he spoke, the Washington Post reported Democratic Senator Mark Warner was trying to assemble a group to ask Mr Biden to step aside, citing two sources close to the effort.

Sky's US partner NBC News reports Senator Warner is focussing on a path forward for Mr Biden, rather than a definitive effort to oust him.

Mr Biden himself admitted he "nearly fell asleep on stage" during the debate, blaming his worldwide travels in the days before.

A 'bad episode'

In his ABC interview, which aired at 1am on Saturday UK time, the president said his performance was a "bad episode" but there are "no indications of any serious condition".

He also rejected seeking an independent medical evaluation during the sit-down with journalist George Stephanopoulos.

"No one has said I need neurological and cognitive tests," he said.

When asked if he is the same man he was when he took office three years ago, Mr Biden pointed to what he said were his successes over his presidency, adding that he is the "most qualified" to lead the Democrats against Trump.

The White House, meanwhile, confirmed on Friday evening Mr Biden checked in with a doctor about a cold "in recent days", but did not undergo a medical exam.

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A handful of donors and business leaders are reportedly unconvinced by what they've seen already, halting funding and looking at possible alternatives.

Even some of Mr Biden's closest political allies, including former Speaker Nancy Pelosi, have raised questions about his health.

Trump, 78, who made multiple false statements from the debate stage in Atlanta, wrongly claimed in a video that circulated on social media he had driven Mr Biden out of the race.