Raleigh, North Carolina - A fired-up Joe Biden came out swinging Friday as he sought to make up for a disastrous debate performance against Donald Trump, insisting he was the right man to win November's presidential election.

Biden's appearance at a campaign rally in the battleground state of North Carolina came amid rumblings in his alarmed Democratic party about replacing the 81-year-old as their nominee.

"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," Biden admitted to supporters in unusually confessional remarks.

"But I know how to tell the truth. I know how to do this job," he said to huge cheers, adding, "When you get knocked down, you get back up."

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Biden's team was in damage-control mode after Thursday's debate when he repeatedly hesitated, tripped over words, and lost his train of thought – exacerbating fears about his ability to serve another term.

He had hoped to allay qualms about his advanced age, and to paint Trump as an existential threat to the future of the US.

But the president struggled to counter his bombastic rival, who delivered an unchallenged reel of false or misleading statements about everything from the economy to immigration.

On Friday, Biden delivered the lines that his supporters wished he could have produced in the televised debate as the election looms a little over four months away.

"Did you see Trump last night? My guess is he set a new record for the most lies told in a single debate," Biden said.

"I would not be running again if I didn't believe with all my heart and soul I can do this job because, quite frankly, the stakes are too high."

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He continued, "Donald Trump is a genuine threat to this nation. He's a threat to our freedom. He's a threat to our democracy. He's literally a threat for everything America stands for."

As the shock over Biden's poor showing registered with Democrats, there was growing talk of how the process might work to find a new candidate before the party's convention in August.

So far, no senior Democratic figure has publicly called on Biden to withdraw, with most toeing a party line about sticking with the existing ticket.

"Bad debate nights happen," Biden's former boss, Barack Obama, wrote on X.

"But this election is still a choice between someone who has fought for ordinary folks his entire life and someone who only cares about himself. Between someone who tells the truth; who knows right from wrong ... and someone who lies through his teeth for his own benefit."

He added that "last night didn't change that, and it's why so much is at stake in November."

Analysts say forcing a change in the ticket would be politically fraught, and Biden would have to decide himself to withdraw to make way for another nominee before the party convention.

A strong – but not automatic – candidate to take Biden's place would be his vice president, Kamala Harris, who loyally defended his performance Thursday while acknowledging he had made a "slow start."

As both candidates returned to the campaign trail, Trump was due to speak at a rally in Virginia.

His allies sought to project calm assurance as the Democrats scrambled.

House Speaker Mike Johnson, a senior Republican figure, said it was clear that Biden was not "up to the job."

"Donald Trump is the only man on that stage that's qualified and capable of serving as the next president. The election cannot get here soon enough."