Biden casts vote in Delaware, calls Trump's Madison Square Garden rally 'simply embarrassing'

Biden responded, "No, this is just sweet."

Biden stepped down from his re-election campaign in July following a poor debate performance that stoked concerns about his health and Democrats' worries about his chances of defeating Trump.

"It's beneath any president but that's what we're used to," Biden said. "That's why this election is so important."

Biden added that Trump puts his own character into question "every time he opens his mouth."

"It's very dangerous," Biden said, of the apparent escalation.

Biden was also asked if he thought Democrats - including Harris - would win.

"I think we will," he said.

The Associated Press contributed to this report.