Former United States vice president Joe Biden says he would not have agreed to replace Hillary Clinton as the Democratic presidential nominee under any circumstances.

Biden told NBC's “Today” show he had decided not to run last year, saying “I would have never done that.”

He was asked about former Democratic National Committee chair Donna Brazile's book, which says she considered replacing Clinton with Biden because of health concerns. Biden said, “I wouldn't have taken” Clinton's place as the party's standard-bearer.

Biden said he was for Clinton, but that he worried about her prospects. He said not long before the election, “It hit me like a tonne of bricks, there was no discussion of issues” in her campaign.

The former vice president further mentioned that he hasn't decided about running in 2020.