Playing the age card against an elderly opponent is a familiar maneuver in American politics.

Joe Biden knows all about that.

When he first ran for the US Senate from Delaware in 1972, he was a 29-year-old challenging an incumbent 33 years his senior. Republican Senator Cale Boggs had first won election to Congress in 1946, and Biden did his best to paint his opponent, politely but pointedly, as washed up.

Boggs was a “helluva nice guy,” Biden would tell reporters, but he “has lost that twinkle in his eyes” and was “just not a fighter.”(In reality, he was a highly decorated World War II combat veteran). Biden speculated about “go[ing] down to the football stadium at the University of Delaware” with Boggs so that voters could compare them on the playing field. He ran ads none-too-subtly painting the incumbent as a relic from a bygone era.

“In 1950 Cale Boggs hoped to make Americans safe from Stalin. In 1972 Joe Biden hopes to make Americans safe from criminals,” declared one ad. “To Cale Boggs an unfair tax was the 1948 poll tax. To Joe Biden an unfair tax is the 1972 income tax,” said another.

Decades later, when Biden was Barack Obama’s running mate, it was John McCain whose age became a political issue. In a TV spot, the Obama/Biden campaign played up McCain’s decades on Capitol Hill, jeering his supposed inability to send an email or use a computer. “Things have changed in the last 26 years,” intoned the narrator, “but McCain hasn’t.”

Now it’s Biden’s turn. He is by a significant margin the oldest man ever elected president. At 79, just 17 months in office, he is older than any of his predecessors were at the end of their presidency. When Ronald Reagan stepped down after eight years in the White House, he was two weeks shy of his 78th birthday and showing unmistakable signs of decline and fatigue. (Five years later, he would be diagnosed with Alzheimer’s.)

Biden, too, shows unmistakable signs of decline and fatigue, and it’s no longer taboo to say so. To be sure, Republicans made much of Biden’s age during the presidential campaign. But now even his Democratic supporters and allies talk about how much he has lost off his fastball.

In a Page 1 story last week, The New York Times noted that in interviews with dozens of Democratic officials across the country, “nearly all” said Biden’s age is causing “deep concern about his political viability.” The president “looks his age and isn’t as agile in front of a camera as he once was,” said David Axelrod, Obama’s former chief strategist.

Writing in The Atlantic a few days later, Mark Leibovich remarked that if Biden had been an airline pilot, he would now be in his 15th year of retirement. Had he been an air-traffic controller, he would have had to retire at 56. Federal regulations mandate compulsory departure times for those jobs because they are “life-and-death tasks that demand peak stamina and mental acuity. The pressure can be crushing [and] burnout is rampant.” Needless to say, the presidency is an even higher-pressure, higher-demand, higher-stakes position. Hence Leibovich’s bottom line: “Joe Biden should not run for reelection in 2024. He is too old.”

A growing number of voters agree. As far back as November, polling data showed that a majority of the public believed that Biden’s age was interfering with his ability to serve effectively as president. In a Harvard-Harris poll last month, 62 percent of respondents said Biden “is showing he is too old to be president” and 53 percent said they have doubts about his mental fitness for office. Among independents, those numbers were even higher — 72 percent (“too old”) and 61 percent (“doubts about his fitness”).

Politically and physically, this isn’t a problem from which Biden can recover. There will be more and more moments in which he appears to be disoriented or abruptly loses his train of thought. He will continue to make unscripted policy announcements that his staff will quickly walk back. As it is, he does almost no extended interviews with journalists, and he holds far fewer press conferences than his last five predecessors. That won’t change.

It is good that Biden’s fellow Democrats are now talking openly about the toll old age is taking on his abilities. That will reduce the instinct to treat the issue as a partisan attack and make it easier for the party to begin searching for a younger standard-bearer for 2024. It will also make it easier for Republicans to acknowledge that Donald Trump — who is only three years younger than Biden — is also too old to run for another term.

Like the incumbent he deposed to win a Senate seat, Biden may be a “helluva nice guy,” but he is visibly past his prime. For the sake of his party and his country, he should take himself out of the 2024 race — not from a lack of ambition but from an abundance of statesmanship.