Donald Trump’s cognitive skills are amazing. So amazing! So great! So much better than any other dumb presidential contender you could mention, at least according to Trump himself, who bragged once again last week of how he had repeatedly aced what he calls “a very hard test for a lot of people”. (It’s thought he means a screening tool for mild cognitive impairment in elderly people.)

Sure, the 79-year-old leader of the free world recently interrupted a cabinet meeting in the middle of a war to ramble on at length about a conversation he supposedly had with the head of the Sharpie pen company over supplying bespoke presidential felt-tips, of which the firm said it could find no record. And made a baffling joke about Pearl Harbor during a press conference in front of an alarmed-looking Japanese prime minister. And called the strait of Hormuz the “strait of Trump”, before adding that that was absolutely deliberate because “there are no accidents with me”. But anyway, to be clear, his mental state is great. The greatest!

Just suppose, however, that it wasn’t. Imagine, purely for the sake of argument, that the 61% of Americans (according to Reuters-Ipsos) who think their president has become more erratic with age and the 56% who don’t think he has the mental sharpness now to deal with challenges (according to recent polling for the Washington Post) were not wrong. Suppose that, much as they did with an octogenarian Joe Biden, millions of Americans had sensed something through their TV screens that genuinely did affect their president’s capacity to send thousands of young soldiers to their potential deaths in the........

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