Already the oldest president in American history, Biden would be 86 if he served out a second term. He has repeatedly said he will run for re-election in 2024, even as many Democrats have questioned whether the party should support a younger candidate instead.

A New York Times/Sienna College poll in July found only 26% of Democratic voters supported renominating Biden for 2024, with age cited as the biggest reason for those opposed.

In September, Biden publicly sought out Jackie Walorski, an Indiana Congresswoman who died in a car accident the previous month, seeming to forget that she had passed away.

"I'm in good health. All my, everything physically about me is still functioning well, so you know, and mentally too," the president, who will turn 80 next month, said in the interview with MSNBC that aired on Sunday.

Biden said he should be judged based on his current vigor on the job, rather than his age, though he acknowledged the issue is a "legitimate" voter worry.

"I'm a great respecter of fate. I could get a disease tomorrow. I could, you know, drop dead tomorrow ... in terms of my energy level, in terms of how much I'm able to do, I think people should look and say - can he still have the same passion for what he's doing?" Biden said.

"And if they think I do and I can do it, then that's fine. If they don't, then they should vote against me - not against me, they should encourage me not to go. But that's not how I feel."