Joe Biden has attacked Donald Trump at a rally a day after the president’s “shocking” performance in a head-to-head debate.

“I don’t walk as easy as I used to, I don’t speak as smoothly as I used to, I don’t debate as well as I used to, but I know what I do know,” said President Biden. “I know how to tell the truth.”

His performance in the debate against Trump on Thursday night was described as an “unmitigated disaster” by some in his own party after he paused and stumbled his way through, prompting calls for him to step down.

“I give you my word as a Biden, I wouldn’t be running again if I did not believe, with all my heart and soul, I can do this job,” he told the rally in North Carolina.

Mr Biden attacked the former president’s criminal record, calling Trump a “one-man crimewave”.

President Biden greets supporters as he arrives in Raleigh. Pic: AP

“My guess is he set a new record for the most lies told in a single debate,” he added, telling the crowd he spent “90 minutes on the stage debating a guy with the morals of an alley cat”.

Donald Trump at rally in Virginia after debating President Joe Biden
Donald Trump at rally in Virginia after debating President Joe Biden

Hours later, Donald Trump was jubilant at a rally in Chesapeake, Virginia.

More on Joe Biden

“Never mind that crooked Joe Biden spent a week at Camp David, resting, working, studying – he studied so hard he didn’t know what the hell he was doing,” Mr Trump told the crowd.

“Biden’s problem is not his age, […] he’s got no problem other than his competence. He’s grossly incompetent,” he added.

Bad debate nights happen

Barack Obama tweeted his support for President Biden on Friday evening, saying: “Bad debate nights happen. Trust me, I know.”

But others remained unconvinced Joe Biden should run for president.

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Joe Biden appears to stall during debate

“I do not think President Joe Biden can be the Democratic Party’s standard-bearer in 2024,” former White House director of global engagement Brett Bruen told Sky News’ Yalda Hakim.

“Last night’s performance was astonishingly bad. You cannot just be strong on the teleprompter,” he said.

But Anthony Scaramucci, former White House communications director, blamed the president’s poor performance on his preparation.

“He wasn’t prepped right for that debate. He’s an older man,” Mr Scaramucci told Yalda Hakim.

“You don’t fill his head with facts and figures he’s never going to remember.”

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Biden v Trump: What you need to know

There have been repeated calls for President Biden to step down.

It’s “time to talk about an open convention and a new Democratic nominee,” one Democratic politician told Sky’s US partner network NBC News.

Read more from Sky News:
Joe Biden: Could the Democrats replace him?

Biden performance among worst in presidential history

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Kamala Harris says Biden had a ‘slow start’ but he ‘pushed facts’ while Donald Trump ‘pushed lies’.

However, while Vice President Kamala Harris acknowledged that President Joe Biden had a “slow start” in the debate, she insisted that he finished “strong”.

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At a Waffle House restaurant in Atlanta after the debate, Biden told reporters he did not have concerns about his performance. “It’s hard to debate a liar,” he said.