Questions about Mr. Biden’s age are increasingly worrying Democratic strategists planning a campaign against likely Republican nominee Donald Trump.
Mr Trump was criticized by NATO’s secretary general on Sunday after suggesting Russia should be “encouraged” to target any member of the alliance that fails to meet its defense spending targets.
A recent ABC News/Ipsos poll showed that 86% of Americans think Mr. Biden is too old to serve a second term in the White House. This included 73 percent of Democratic voters.
Mr Biden’s allies condemned the report’s remarks as inappropriate and unfair.
On Sunday, his personal attorney said he had raised concerns with the special prosecutor and attorney general about what he considered derogatory and unnecessary searches in the president’s memory.
“It’s a report that’s gone off the rails,” Bob Bauer said on CBS’s Face the Nation Sunday. “It’s a lousy piece of work.”
Jill Biden, the first lady, defended her husband in a note to his campaign donors and questioned whether it was meant to “score political points.”
Mrs. Clinton also said she supported Mr. Biden’s campaign for a second presidential term because of his “merits.”
“Once you’ve said that, you also have to talk about what’s at stake in this election,” Clinton said. “And I’m for Joe Biden because of his merits.”
“I think he did a very good job as president,” she added.
