Hillary Clinton has stepped into the public relations meltdown over Joe Biden's fitness for office, admitting the 81-year-old's age is "a legitimate issue."

Clinton, a campaign surrogate for Biden who lost to Donald Trump in 2016, advised Biden to embrace his age as a selling point.

“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,” Clinton told MSNBC’s Alex Wagner.

Clinton kicks Biden while he's down...

Biden's age has come into sharp focus after Special Counsel Robert Hur's report, which described Biden as an "elderly man with a poor memory."

The report concerned Biden's mishandling of classified information - a topic Clinton, who escaped charges over an illegal e-mail server, knows something about.

Democrats have furiously blasted Hur's comments as "gratuitous" editorializing while comparing Hur's work to James Comey's handling of Clinton's email saga, which similarly ended with no criminal charges.

Biden defended himself against charges of cognitive decline at an irascible press conference that many have described as an unforced error. Still, Clinton thinks Biden should make himself more visible.

“I’m for Joe Biden for reelection on the merits because I think he’s done a really good job as president,” Clinton said. “So, I think he should continue to get out and campaign.”

Clinton's advice

Clinton also described age as a "legitimate issue for Trump who’s only three years younger," but voters overwhelmingly do not see age as a significant issue for the vigorous 77-year-old.

"I think Biden also should lean into the fact that he’s experienced and that experience is not just in the political arena. It’s like, the stuff of, you know, human experience,” she said. “I think he should be willing to really pull that out … and I think he should care more about it.”

The New York Times published a scathing editorial urging Biden to aggressively confront the issue and put voters' concerns at ease.

"He must do better — the stakes in this presidential election are too high for Mr. Biden to hope that he can skate through a campaign with the help of teleprompters and aides and somehow defeat as manifestly unfit an opponent as Donald Trump, who has a very real chance of retaking the White House.”

The White House is still refusing to commit to having Biden take a cognitive test, despite overwhelming popular consensus that Biden is fading mentally.