Vice President Kamala Harris said in a Wall Street Journal interview published on Monday that she is ready to step up if President Joe Biden cannot continue to serve, though she defended Biden’s mental acuity and capacity to do the job after Special Counsel Robert Hur described Biden as an “elderly man with a poor memory.”

The special counsel’s report, which explained why Hur is declining to prosecute the president for his handling of classified documents, sparked a new round of concern and questions about the 81-year-old Biden’s memory and the limits he faces in his ninth decade. If he secures and finishes a second term, Biden would be 86.

“I am ready to serve. There’s no question about that,” Harris told the Journal aboard Air Force Two last week. Those who see her work, the 59-year-old said, walk “away fully aware of my capacity to lead.”

On Friday, Harris called Hur’s report “gratuitous, inaccurate and inappropriate” and said its assessment of Biden’s mental state “could not be more wrong on the facts and, clearly, politically motivated.” Biden himself angrily defended himself from the report’s characterization last Thursday.

"I’m well meaning, I’m an elderly man, and I know what the hell I’m doing," Biden said at a press conference.

An ABC News/Ipsos poll released Monday and conducted after Hur’s report found 86% of Americans think Biden is too old to be president another four years. Former President Donald Trump, 77, was viewed as too old by just 62%. Among independents, 91% thought Biden was too old and 71% thought the same of Trump.

A national poll by NBC News last week found 76% of respondents had either major or moderate concerns about Biden’s mental and physical health. Another 13% said they had minor concerns. Comparatively, 48% said they had major or minor concerns about Trump’s health, with another 17% expressing minor concerns. Other national polls since the start of the year have broadly given Trump an advantage over Biden in a hypothetical general election matchup.

Despite the unlikelihood of Democrats moving to replace either Biden or Harris — who has traveled the country encouraging Black voters to once again support their ticket — both leaders have remained largely unpopular.

On average, Biden’s approval rating is around 39%, while around 56% disapprove of his job performance — equal to an all-time low for him since entering the White House, according to polling aggregator FiveThirtyEight. Harris’ average approval rating is a touch below the president’s, sitting at 37.5%, with 53.5% disapproving. 

While Harris, the first woman and Black vice president, would succeed Biden in the White House if he could not complete his first term, it would be more complicated for her to secure the nomination in the unlikely scenario where Biden opts not to run for reelection after all.

Nearly every state’s ballot deadline for the primaries has passed — as have Democratic contests in New Hampshire, South Carolina and Nevada. Biden’s token primary challengers in Minnesota Rep. Dean Phillips and spiritual leader Marianne Williamson have lost by overwhelming margins so far. Williamson dropped out last week and polling suggests Phillips, who has centered his campaign on Biden’s age and declining popularity, is not on the path to improve on his prior performances.

If Biden chooses not to pursue the nomination after winning the primary virtually unopposed, Democratic National Committee delegates would vote at the August convention to replace him, according to DNC rules. Harris would presumably be among the top contenders, but there is no bylaw and little precedent that would require her to succeed him as the party’s leader.

Despite her lack of popularity, the former California senator has seen her public portfolio expand in recent months to include gun violence policy and a role in U.S. foreign policy in the expanding Middle East conflict sparked by the Israel-Hamas war and the bombardment of Gaza.

“I was in almost every meeting with the President in the hours and days that followed [the Oct. 7, 2023, Hamas attack on southern Israel.] Countless hours with the Secretary of Defense, the Secretary of State, the heads of our intelligence community,” Harris said on Friday. “And the president was in front of and on top of it all, asking questions and requiring that America's military and intelligence community and diplomatic community would figure out and know” the specifics of the situation on the ground.

Harris has also taken point on the 2024 campaign’s abortion rights messaging as restrictions have poured in across the country since the undoing of Roe v. Wade by the Supreme Court. She is uniquely qualified for leadership on a key issue, she argued in the interview, framing it as an example of where she can exemplify she has what it takes to be president and make an electoral and policy argument to the American public.

“I do believe that the majority of people have an empathy gene,” she said during the interview aboard Air Force Two. “And the more they realize what has actually been happening since the Dobbs decision came down, the more open they are to consider the fundamental point, which is: Should the government be telling a woman what to do?”

Discussing women’s reproductive health, Harris often draws from her experience as a prosecutor on sexual assault cases and as the attorney general of California, and lays the blame for the overturning of Roe v. Wade at Trump’s feet. For his part, Biden’s likely GOP challenger proudly takes credit for it at rallies and campaign appearances.

Despite Biden’s insistence he will continue to run for reelection, some Republicans have speculated without evidence that Harris — or other Democrats like California Gov. Gavin Newsom and former First Lady Michelle Obama — is secretly pulling the strings or setting herself up to assume the presidency.

“We will have a female president of the United States, hands down,” former U.N. Ambassador Nikki Haley said in Los Angeles last week. The last major challenger to Trump in the GOP primary has made his and Biden’s age and mental acuity central to her argument on the campaign trail. “It is either going to be me or it is going to be Kamala Harris.”