HERE are some truths about ageing – your body stops doing things it once never thought twice about. Your mind may still function fine but the retrieval system slows down.

I don’t think modern politics is ready for a leader who says “hang on a minute, the name will come to me!” As witness Joe Biden’s confusing of the Mexican and Egyptian presidents.

In last week’s debate with Donald Trump on CNN, Biden said he beat Medicare instead of what he meant, that he saved it. That is shocking. Not least as it gave the odious Trump person a feed line he greedily grabbed.

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Yet in a sense Biden’s Democratic Party has become a mirror image of the Republicans, in that nobody has the bottle to tell him unwelcome truths outside of The New York Times. Least of all, it seems, his wife.

Jill Biden seems an entirely good thing. But she congratulated her husband post-debate as if her dimmest student had suddenly learned to spell. The next night, she invited the rally crowd to celebrate because Joe managed to navigate an autocue. It’s a whole lot easier to read a speech than to respond spontaneously to unrehearsed questions. As last week dismally proved.

As you age, your energy levels become irritatingly depleted. With something you once would have contemplated doing in a heartbeat, you start to calculate all kinds of odds as to what is realistically achievable.

I am not as old as Joe Biden. But I am old enough to know that nobody gets a free pass as they age. Even if you encounter no serious health issues – and Biden has had two aneurisms – you will slow up in mind and body. That’s a sad but certain fact of living and dying.

I once had an elderly American friend who advised me: “Old age is not for sissies.” She knew of what she spoke. She was mightily irritated when, on medical advice, her family relieved her of her car keys.

Old age is not for political leaders either. Certainly not for the top job which entails going toe to toe mentally with other prime ministers and presidents who may be half your age. Sure they won’t have the same experience to draw on but neither will they forget where they are and why, as Biden appeared to at the D-Day “family album” shot.

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The awful truth is that no matter how many sharp-suited, smart young advisers surround you, there are many times when a president will be exposed to the full glare of global attention all on his or her lonesome.

‘I know how to tell the truth,” Biden said, the evening after the debate debacle. “I know right from wrong.”. “I know how to get things done.” You would hope so, in that you are president.

And you would hope these qualities are not unique, even if your current opponent struggles to stay on nodding terms with the facts. (Only Donald Trump seems able to make Boris Johnson seem truthful by comparison.)

Sadly there is no American equivalent of the men in grey suits who can advise someone that it really would be best if they left the stage. No back-bench committee to whom dissatisfied colleagues can dispatch notes of no confidence in the boss. Another rather dispiriting thought.

Suppose Biden were to win again despite the current polling. He would take up office in his 80s and, if he survived, would be just four years off 90 at full term. Actuarially speaking, he might well not survive.

In which case the US would be handed a vice-president with whom they seem even less enamoured. America has had veeps visited on them before. It’s difficult to call any of them an unqualified success.

One of them, Jack Kennedy’s vice-president, actually pulled out of going for a second term in the same year as the election. And whatever you think of Lyndon Baines Johnson – and he did pass historic civil rights legislation – he was considerably fitter when he quit than Joe Biden appears to be right now.

According to everything I’ve read, only Joe and Jill Biden can pull the plug on his bid for a second term. If she has a modicum of sense, Jill could figure that she might have a fair few years of relative privacy to spend with a man whose last, and greatest gift to the country he has long served, would be to go before death or disease claim him.