Biden declares he is 'staying in the race,' insists he can beat Trump

US President Joe Biden insisted on Friday that he would not drop his bid for a second term, even as calls for him to bow out grow following his damaging debate performance against Republican rival Donald Trump.

"Let me say this as clearly as I can, I'm staying in the race. I'll beat Donald Trump," he forcefully declared to a crowd of chanting supporters at a campaign event in the state of Wisconsin.

Pressure on Biden to step aside as the Democrat's 2024 presidential candidate has been growing from within his own ranks since he faced off against Trump at a 90-minute televised debate on June 27.

During the showdown, a raspy-voiced Biden fumbled his sentences, seemed to lose his train of thought and often struggled to get his words out.

The fallout was quick and severe as a chorus of political pundits declared his campaign to be in deep trouble. In the days since, Democrats have been in crisis mode amid new opinion polls showing 81-year-old Biden losing more ground to 78-year-old Trump.

"I learned long ago, when you get knocked down, you get back up," Biden said at the rally in Madison, Wisconsin. "I'm not letting one 90-minute debate wipe out three-and-a-half years of work."

"Let me ask you: You think I'm too old to beat Donald Trump?" Biden, who is the oldest president in US history, asked the cheering crowd.

"No!" they yelled back.

"I can hardly wait," the president said.