I know how to do this job, defiant Biden says during campaign rally

President addresses enthusiastic crowd in North Carolina amid calls for him to step aside

US President Joe Biden at a campaign event in Raleigh, North Carolina. Bloomberg

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US President Joe Biden on Friday acknowledged his advanced age and declining speaking abilities, but said he knows “how to do this job”, pushing back against accusations that he was not capable of running for another term in office.

Mr Biden was speaking to supporters during a campaign rally in North Carolina in his first public comments since his dismal debate performance on Thursday.

“I know I'm not a young man, to state the obvious,” he said, smiling to loud cheers from the crowd.

“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,” he continued, “but I know what I do know, I know how to tell the truth.”

“I know how to do this job.”

Mr Biden, 81, is facing a brutal reckoning the day after he repeatedly fumbled during the first debate against his likely Republican rival Donald Trump.

Trump, only three years his junior, appeared much more energetic than Mr Biden, who in the first few minutes of the debate, appeared to lose his train of thought.

His voice was hoarse and at times inaudible. His team later said he had a cold.

The fallout on Friday included panicked reactions, including from Democratic pundits who suggested that Mr Biden should step aside and allow for a younger suitable candidate to run instead.

Strategists began floating lists of possible replacements, which have included Vice President Kamala Harris.

Although Mr Biden won the Democratic primary elections earlier this year, he has not yet been named the official candidate for his party.

That is scheduled to happen during the Democratic National Convention, which will take place in Chicago in mid-August.

But Mr Biden has given no indication that he intended to step aside.

Addressing his poor performance directly, he said: “I know, like millions of Americans that when you get knocked down, you get back up.”

Trump appeared at a rally in Virginia where he declared that he had won the debate, and delivered a series of insults focused on Mr Biden's competence.

“As you saw on television last night, we had a big victory against a man that is looking to destroy our country,” he told the crowd.

He then mocked how Mr Biden had spent the week preparing for the debate at Camp David.

“He studied so hard that he didn't know what the hell he was doing,” he said to cheers.