The main Nuremberg trial ended, Winston Churchill warned of an iron curtain descending across Europe, It’s a Wonderful Life received its premiere and, at Jamaica hospital in the borough of Queens, New York, Donald John Trump was born.

It was 1946, also the birth year of George W Bush and Bill Clinton, but on Sunday the current US president celebrates his 80th birthday in a style uniquely his own. Trump will stage a night of cage fighting on the once-pristine White House south lawn as part of events marking the 250th anniversary of US independence.

The blend of visceral bloodsport with political spectacle under metal scaffolding may offer brief respite for a president also consumed with an unpopular war, rising inflation, plunging poll numbers and a foe not even he can bully, bomb or outrun: Father Time.

“Donald Trump has been showing signs of his age for quite some time,” said Tara Setmayer, a former Republican communications director on Capitol Hill. “It’s on display almost daily as he struggles to stay awake during official meetings, he is more irritable and going on rage tangents and throwing temper tantrums when he doesn’t get his way. These are not signs of a well-adjusted adult approaching 80 years old.”

Trump is the oldest US president sworn into office and, some critics say, showing alarming evidence of decline as he becomes an octogenarian, a status that more than half his predecessors never achieved and that found Gerald Ford playing golf, Jimmy Carter immersed in humanitarian work and Ronald Reagan organising his memoirs.

A Reuters/Ipsos poll in February found 61% of Americans thought Trump had become more erratic with age, and another survey in April showed a majority concerned about his temperament and mental sharpness.

The physical evidence is increasingly difficult for his aides to conceal, though they aggressively project a narrative of vigour. The president has been photographed with bruised hands and swollen ankles, ailments his medical staff continually brush off as a “slight” issue. He sees 22 medical specialists, an apparent new bar for presidents.

His public calendar has grown notably sparse, dominated by hours of nebulous “executive time” and behind-closed-doors policy meetings. After a flurry of travel early in the year, he has largely retreated to the cocoons of the White House and his clubs in Florida and New Jersey since launching the Iran war in February.

Then there is the sleeping. Trump has increasingly been caught on camera apparently nodding off at public events, most recently at an NBA basketball finals game at New York’s Madison Square Garden. When clips of his shut eyes go viral, his aides claim he was merely blinking or listening intently.

The White House spokesperson Davis Ingle has insisted that Trump remains “the sharpest and most accessible president in American history”. The president himself frequently boasts of “acing” cognitive tests that would have flummoxed past presidents.

But to observers the spin is not only unconvincing but counterproductive. Kurt Bardella, a political commentator and former congressional aide, said: “It’s not surprising that someone who’s on the doorstep of being octogenarian is showing signs of ageing. Father Time is undefeated: that applies to everybody including Donald Trump and I would have more confidence in him as commander-in chief if he would just admit that rather than try to hide it.”

Bardella added: “Hiding it is a sign of weakness. Being transparent, forthright, honest about it would actually be a sign a strength. The fact the White House seems to be going to all these ridiculous and laughable measures to try to convince us that he’s not actually ageing is insulting to American people, it’s idiotic, it reeks of desperation, and it makes everyone believe that there’s more going on than meets the eye. And what meets the eye isn’t that great. Secrecy breeds mistrust.”

If that complaint sounds familiar it is because Trump’s predecessor, Joe Biden, who was 78 when he took office in 2021, faced similar charges. White House officials were accused of covering up Biden’s failing capacities. Jill Biden, the former first lady, wrote in a new memoir that she feared her husband had had a stroke when he delivered a feeble debate performance that forced him to abandon his campaign for reelection.

Bill Whalen, a policy fellow at the Hoover Institution thinktank in Stanford, California, said: “It’s very difficult, if not a double standard, for every Democrat to criticise Donald Trump as too old and too out of touch, with Democrats having basically zipped their lips in 2024 and not dared say the same about Joe Biden. In this age of whataboutism it is another bad case of whataboutism.”

Trump’s critics, however, reject the comparison, contending that the concerns around him are greater by orders of magnitude.

Setmayer, who now runs the Seneca Project, a female-led political action committee, said: “There is a fair discussion to be had about a president’s physical and emotional condition, no matter what age they are. However, if Joe Biden was exhibiting the same level of cognitive incoherence and physical decline in public the way Donald Trump currently is, the apoplexy on the right would be palpable.”

Such commentators argue that Trump’s already volatile psyche is fraying as his stamina wanes. Even with the nation at war with Iran and citizens strained by the cost of living, he touts a $1.4bn White House ballroom, revamp of the Lincoln Memorial reflecting pool and plans for a huge triumphal arch.

His speeches, which have long been rife with non sequiturs and long stories, increasingly ramble, repeat and take baffling tangents. He is prone to more scattergun statements that give Republican strategists heartburn, such as “I don’t think about Americans’ financial situation”, “I don’t care about the midterms and “I love the inflation”. At dead of night he pushes election conspiracy theories and torrents of AI slop on social media.

Nowhere was this more evident than during an explosive confrontation last week with the journalist Kristen Welker on the NBC show Meet the Press. Factchecked on his false claims of election rigging, Trump flew off the handle and said Welker was either “crooked” or “stupid”, then abruptly ended the interview: “Let’s call it quits because I’ve had enough. Thank you darling. Have a good time.”

Larry Sabato, the director of the Center for Politics at the University of Virginia, watched the broadcast with genuine alarm. “The man was out of control,” he said. “How he kept himself from having a heart attack or stroke, I don’t know. You saw his face. He’s orange at the best of times but he was oscillating between red and orange. I really did think he was going to have a heart attack.”

As for Trump’s penchant for napping, Sabato offers a silver lining of sorts. “You shouldn’t laugh but it’s the only time he looks peaceful,” he quipped. “It’s the only time his mouth is shut and he’s not saying something obnoxious, so I’m always grateful when he nods off.

“But what that proves to me is there’s nobody in his family or his staff that can control him in any way. There’s no way somebody his age should be staying up practically the whole night or intermittently waking up and sending out these crazy memes – dozens of them sometimes. It’s unbelievable.”

The prospect of such a man having access to the nuclear codes would typically prompt discussion of his cabinet invoking the 25th amendment to the constitution to remove him from office. No one expects Trump’s team of loyalists to even remotely consider such an option. Republicans in Congress have shown flickers of dissent lately but preserved a conspiracy of silence around the age issue.

Trump is therefore expected to remain in office for his 81st and 82nd birthdays, potentially as a lame duck president facing political mortality if Democrats win one or both chambers of Congress. For many people such age brings wisdom, wistfulness and a softening of hard edges, but for Trump it seems only to exacerbate his character and make him more truly himself.

Gwenda Blair, a Trump biographer, said: “Any sign of grace? Perspective? Those have not emerged. Those are the kind of rewards of being older that many people experience but not him. Instead he’s doubling down on the exact same behaviour patterns that he has always had: what’s in it for me and how can I get the maximum out of it and then more than that?”

The questions over the judgment and temperament of the world’s most powerful man, and the potential risks to the global order, will only grow louder in the coming years, according to Larry Jacobs, the director of the Center for the Study of Politics and Governance at the University of Minnesota.

“The recklessness of decisions, the failure to think in a logical evidence-based way, the acting on impulse, the losing track of reality versus the talking points – all these things are being accelerated by Trump’s age. Most presidents’ skill set begins to fade as they age; Trump has got such a limited toolkit that it’s putting him over the edge.”

Jacobs warned: “America and the world are in for a frightening two years. Trump has too much power for someone with so little connection to reality. Age is making Trump an even more dangerous president.”