STORY: BIDEN: "I know, like millions of Americans know, when you get knocked down, you get back up."

U.S. president Joe Biden gave no sign of dropping out of the presidential race during a rally in North Carolina on Friday...

...a day after a feeble debate performance against his Republican rival Donald Trump that dismayed his fellow Democrats.

BIDEN: "I don't walk as easily 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. I know how to tell the truth. (AUDIENCE CHEERS)"

Biden's verbal stumbles and occasionally meandering responses during the debate heightened voter concerns that he might not be fit to serve another four-year term...

even prompting some of his fellow Democrats to wonder whether they could replace him as their candidate for the Nov. 5 election.

Trump: "He studied very hard. He studied so hard that he didn't know what the hell he was doing."

Meanwhile Trump - who put forward a series of falsehoods throughout the debate - appeared to take a victory lap Friday afternoon at a dueling rally in Virginia.

"He got the debate rules that he wanted. He got the date that he wanted. He got the network that he wanted..."

[FLASH]

"We need more substance and voters deserve more substance."

Julia Azari is a political science professor at Marquette University.

"...the proof there is going to be in kind what the polls look like next week. More than, more than anything, a sort of --- did this move the needle? [FLASH] it's very hard to take this out of the context of what's going on with Trump. You know, I think no matter how badly Biden did, the felony convictions, -- a much more significant story, a much more substantive story - that didn't change the polls very much."

The Biden campaign said it raised $14 million on Thursday and Friday and posted its single best hour of fundraising immediately after the debate.

The Trump campaign said it raised $8 million on debate night.

Biden, already the oldest American president in history, faced only token opposition during the party's months-long nominating contest.

He has secured enough support to guarantee his spot as the Democratic nominee.

Trump likewise overcame his intra-party challengers early in the year, setting the stage for a long and bitter general election fight.