Donald Trump has never looked more like a son of Scotland than when he arrived at his Menie Estate golf course at Balmedie this week. Maybe it was the bobble hat. It is hard to look like an international supervillain when you are sporting a pompom.

“It’s great to be home,” the former President told reporters, once again reminding the assembled media of his Scottish roots on his mother Mary Anne MacLeod’s side. Like any true Scot he had dressed for the weather, caring not a jot if wearing a tea cosy on his head made him look old. At the sprightly age of 76, he doesn’t need to worry about such things. Whatever else he has going on, age is among the least of his concerns.

Not so for the man he is likely to be running against for the US presidency next year. At 80, President Joe Biden’s age is becoming the central issue of the 2024 race, much to his dismay and his opponents’ delight, and it is a problem that is only going to get worse.

His age has been a factor before, but officially launching his campaign for re-election, as he did last week, has made his critics bolder. Forget all that elephant in the room, kid gloves, let’s have a mature debate about this, stuff. His opponents are now openly warning that if re-elected in 2024 he will die in office, leaving America in the hands of his vice-president, Kamala Harris.

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Nikki Haley, a Republican candidate who announced her run in February, told Fox News recently: “I think we can all be very clear and say with a matter of fact that if you vote for Joe Biden you really are counting on a President Harris, because the idea that he would make it to 86 years old is not something I think is likely.” Happy birthday to you too Ms Haley, 51.

Steve Hilton, a former Downing Street adviser to the Tories turned Fox News show host, declared in a British newspaper at the weekend that the US President “is now clearly senile”. Just as well Mr Biden is giving the Coronation a miss.

He has tried various ways to deal with the age question, not always with success. His efforts to look like a young man in a hurry have tended to end in stumbles, verbally and physically. Obvious irritation hasn’t worked, nor have attempts at Reaganesque charm.

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He keeps trying though. At the White House Correspondents’ dinner last weekend, he quipped: “You might think I don’t like Rupert Murdoch. That’s simply not true. How could I dislike the guy who makes me look like Harry Styles?”

The media mogul makes a fitting target, not just because it is his news empire that has been going after Mr Biden’s age with such glee. Mr Murdoch is 92, but you will never hear anyone in his employ publicly questioning whether he is up to the job. They wouldn’t dare. So why do it with Mr Biden?

There is a difference though. For a start, Mr Murdoch, for all his power and influence, doesn’t travel with the nuclear football in his luggage. Yet America and the world had four years of Donald Trump being within a couple of feet from the means to launch a nuclear attack, but somehow everyone managed to sleep at night.

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Being US President remains one of the most powerful jobs in the world, but the way it is presented does not always match the reality. The President is one person at the head of a vast organisation. Countless decisions are made in his name every day. Any failings of the man himself count, of course they do, but not to the extent they would if he was in solo charge.

America is not alone in wanting its leaders to appear hale and hearty, if not superhuman. Down the years the truth about various presidents’ health has been hidden for fear of making them seem weak at home and abroad. Would FDR in his wheelchair ever have made President? It would have been impossible then, and highly unlikely now.

Some of the attacks on Mr Biden are grossly unfair. The way he speaks, for example, is to mask a stutter. He is to blame, however, in one respect. There would be far less concern about his age if he had a vice-president that the majority of Americans knew and trusted. Kamala Harris was important in securing Mr Biden’s first win, and by the number of times she appears in his re-election video she will play a key role in his bid for a second term. Yet between times she has struggled to find a role that makes her look competent, never mind a president in waiting.

Her boss did not help by handing her some of the toughest jobs in government, tackling illegal immigration being one of them, and he has not been as generous at sharing the spotlight as Barack Obama was with him. That is changing, and not before time. With a year and a half out from the next election there is scope for Ms Harris to shine in her own right.

Whether she can make the most of the chance remains to be seen. She has been tested and at times found wanting. Like Mr Biden, she had a relatively easy time of it at the last election. Covid meant that both of them were not given as much media scrutiny as would usually be the case. Mr Biden in particular was allowed to stay out of sight at home, few media questions asked. That will not and should not happen again.

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As for Mr Trump, we can expect him to show no mercy to his opponent when it comes to age or anything else. He certainly didn’t last time. But he too is vulnerable on the question of getting older. He looked fighting fit enough on the golf course on Monday, but four years in office and four years out nursing a grudge about a “stolen” election that never was, would take its toll on the fittest of folk. And that’s without the court cases, civil and criminal, he is involved in.

Both men have failed to plan for their succession. They are hardly alone in that, as Scotland knows too well. Barring a twist in the tale, the world is about to witness a real-time experiment in the effects of ageing on a person’s fitness for office. Good luck to us all.