Hillary Clinton said Joe Biden’s age is a “legitimate” issue amid concerns about the US president’s fitness for office.
The former Democrat presidential nominee added that the White House is aware of this.
Ms Clinton told MSNBC: “I talked to people in the White House all the time, and you know, they know it’s an issue, but as I like to say, ‘look, it’s a legitimate issue’.
“It’s a legitimate issue for Trump who’s only three years younger, right?” Ms Clinton added. “So it’s an issue.”
The interview was recorded on Wednesday, the day before Robert Hur, the Department of Justice’s special prosecutor, published his report investigating Mr Biden’s handling of classified documents.
The report described the 81-year-old president as a “well-meaning, elderly man with a poor memory” which was “hazy”, “fuzzy”, “faulty” and having “significant limitations”.
It also noted he could not recall defining dates in his own life such as the year his son Beau died or when he served as vice president.
Both Mr Biden and the White House rejected the characterisation, with the president insisting: “My memory is fine”.
“I know what the hell I’m doing,” he added.
Questions about Mr Biden’s age are a growing concern for Democrat strategists planning an election campaign against likely Republican candidate Donald Trump.
On Sunday, Mr Trump was criticised by the Nato general secretary after suggesting Russia should be “encouraged” to target any alliance member that fails to meet defence spending targets.
A recent ABC News/Ipsos poll showed that 86 per cent of Americans believe Mr Biden is too old to serve a second term in the White House. That included 73 per cent of Democrat voters.
Mr Biden’s allies condemned the report’s remarks as inappropriate and unfair.
On Sunday, his personal lawyer said he registered concerns with the special counsel and the attorney general over what he said were pejorative and unnecessary digs at the president’s memory.
“This is a report that went off the rails,” Bob Bauer said on CBS’ Face the Nation Sunday. “It’s a shabby work product.”
Jill Biden, the First Lady, defended her husband in a note to his campaign donors and questioned whether it was intended to “score political points”.
Ms Clinton also said she is endorsing Mr Biden’s campaign for a second presidential term because of his “merits”.
“Once you say that, you need to also talk about what is at stake in this election,” Ms Clinton said. “And I’m for Joe Biden because of the merits.”
“I think he has done a really good job as president,” she added.