Age isn’t just a number. It’s a profound and growing problem for Biden.

Special counsel Robert Hur jolted the presidential campaign Thursday with a withering assessment of Joe Biden's mental acuity, drawing the president’s biggest political liability firmly into the public conversation.

While Biden’s age is a major concern for voters in polling, top Democrats have danced around the issue, keeping their concerns mostly private. But Hur’s description of Biden, 81, in an official report as a “well-meaning, elderly man with a poor memory” may force a new reckoning for the president.

Investigators found insufficient evidence to charge Biden for mishandling classified documents during his time as vice president but wrote his memory “appeared to have significant limitations” and that “he did not remember, even within several years, when his son Beau died” in 2015. Biden could not remember when he was vice president or the details of a debate about sending additional troops to Afghanistan, they said.

That scathing description came just as Biden’s aides were trying to explain away the president’s most recent verbal gaffes — in which he mixed up the heads of state and recalled recent conversations with world leaders who died long ago.

During a pair of New York fundraisers on Wednesday night, Biden twice described conversations he said he had in 2021 with European leaders at the G7 meeting in the U.K., which took place just months after the U.S. Capitol insurrection. At both Manhattan events, Biden said that former German Chancellor Helmut Kohl, who died in 2017, had asked him about the Jan. 6 riot and his reaction if people stormed the British Parliament and killed officers "to stop the election of a prime minister."

And just days earlier, during a campaign event outside of Las Vegas, Biden mixed up François Mitterrand, the former French president who died in 1996, for French President Emmanuel Macron.

Democrats have defended Biden but also questioned the age and fitness of Biden’s likely Republican rival, Donald Trump, himself facing an indictment over his handling of classified materials.

Beyond his recent high-profile mix-up of Nikki Haley and Nancy Pelosi, Trump, 77 has repeatedly said he is running against Barack Obama, and not Biden, and that he feared that the nation may soon enter World War II, a conflict that has been over for nearly 80 years.

Biden's mistakes underscore what critics say are the most persistent political threats to the president’s reelection bid: his age and the fear among voters that he is not mentally fit to hold office again.

“If you turn on Fox News, they’re talking about a bumbling, fumbling Joe Biden. If you go on TikTok, Instagram, there are tons of videos making fun of his age,” said a Democratic donor adviser, granted anonymity to discuss a sensitive issue. “It’s just consistently out there, so the more this happens, the more it feeds it.”

Then came Thursday’s release of the special counsel report. It noted investigators found insufficient evidence to charge the president for mishandling classified documents during Biden’s time as vice president. But it also said that Biden's memory “appeared to have significant limitations” and that “he did not remember, even within several years, when his son Beau died” in 2015. And it said that Biden could not remember when he was vice president or the details of a debate about sending additional troops to Afghanistan.

After the report was released, White House lawyers disputed Hur’s characterizations of Biden’s memory, and argued that he had gone outside his scope and remit. They said he was gratuitous in his focus on the president's memory. Republicans were biting. Speaker Mike Johnson, Majority Leader Steve Scalise (R-La.), GOP Whip Tom Emmer (R-Minn.) and Conference Chair Elise Stefanik (R-N.Y.) in a joint statement, said the comments on Biden’s memory were among the report’s “most disturbing parts.”

“A man too incapable of being held accountable for mishandling classified information is certainly unfit for the Oval Office,” they added.

Polls have consistently shown deep voter concerns about Biden’s age. A new NBC poll released this week found a combined 76 percent of voters say they have major (62 percent) or moderate (14 percent) concerns about Biden lacking the necessary mental and physical health to be president for a second term. Perhaps most worrisomely for the president, 81 percent of independents and 54 percent of Democrats say they have major or moderate concerns about Biden’s fitness for a second term.

On whether they have the same concerns about Biden’s likely GOP opponent, Donald Trump, the poll found 48 percent of voters said they did.

The former president also has made a series of recent gaffes. When he confused Haley for Pelosi, it prompted Haley, his lone remaining GOP primary rival, to suggest that Trump was “in decline” and no longer up for the job.

Before the release of the special counsel report, the White House was asked about the president’s misstatements about the foreign leaders — and dismissed them as nothing more than slips. “As it relates to the names and what he was trying to say, many people, elected officials, many people, you know, they can misspeak sometimes,” White House press secretary Karine Jean-Pierre said Thursday.

Biden campaign spokesperson Kevin Munoz argued “it is very clear what will matter most to voters” in November.

“Like we did in 2020, we'll remain focused on those issues that matter to families and how it's only because of President Biden's deep experience that Democrats up and down the ballot are able to run on such a historic and popular agenda,” Munoz said in a statement.

Biden has previously made other errors involving the deceased. Most infamously, he mistakenly called out for Rep. Jackie Walorski at a September 2022 event, though the Indiana Republican had died in a car crash the month before. Last year, Biden mixed up Chinese President Xi Jinping with Deng Xiaoping, the Chinese leader who died in 1997.

Both Biden and Trump “are vulnerable to age-related mistakes,” said Dan Sena, a Democratic consultant who led the Democratic Congressional Campaign Committee in 2018. “But I don’t completely buy into the ageism argument against either of them — that making gaffes will decide this. It’ll come down to the larger meta-narrative about those who are looking backward and those who are looking forward.”

Even so, “I don’t envy the management position they’re constantly in,” Sena added. Biden’s “ability to connect is one of his greatest strengths, but at the same time, it exposes some of his vulnerabilities.”

Democrats argue that the president’s age is baked in for most voters, who are keenly aware of his advanced age. They point to Biden’s victory in 2020, when he was 77, as evidence he has already overcome the issue.

“If [Republicans] spend all this money on saying he’s old and his age makes him out-of-touch, who does that move? Who is on the fence on that issue? People have already made up their minds on this,” said Kevin McKeon, a Democratic consultant.

The Biden campaign has, at times, used humor to try to neutralize the issue, a strategy Democratic donors have urged him to lean into. On his 81st birthday, Biden’s campaign posted a photo of the president in front of a blazing birthday cake, joking about his “146th birthday.”

Others, like Democratic strategist Mark Longabaugh, believe that “the president has to just go on being the president, showing he has the vigor to be the president,” but that means “some of these mistakes are going to occasionally happen.”

Biden’s pitch in 2020 was that he was the one Democrat who could beat Trump and the incumbent president has privately suggested that he believes that holds true again for this November.

But his age prompted a presidential primary challenger. Rep. Dean Phillips (D-Minn.) launched a long-shot bid against Biden that is entirely centered on how the president’s age weakens Democrats’ chances in beating Trump.

“I’m attacked for being honest and saying the quiet part out loud — the part DC insiders only do in private,” Phillips posted on X, including a clip of Biden from earlier this week, when he appears to forget the name of Hamas, when answering a question about the Israel-Hamas conflict.

“But shame on all of you pretending everything is ok. You are leading us — and him — into a disaster, and you damn well know it,” Phillips wrote.

Those in Biden’s inner circle note that fatigue forces Biden to expend more energy combating his lifelong stutter — and contribute to verbal slips.

But while many in Biden’s orbit bristle at the narrative about his age, they also believe they can neutralize it. They argue that voters don’t make their decisions about whom to support based on age, and instead are more concerned about a candidate’s values and accomplishments.

Biden’s advisers also make the case that he was slammed by Trump and his GOP allies over his age and mental fitness during the 2020 campaign, and that they overcame those attacks in part by pointing to his experience. Now, they said, they can point to major legislative victories as part of an updated plan as well as a robust travel schedule that compares favorably to his predecessors and includes two recent stops in war zones.