Never mind leading the free world, if Donald Trump were your ageing father, when would you take away his car keys?

Presidential decisions can mean life or death for millions around the world, that’s why constitutional safeguards exist. But do they work in practice? 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...

By Gaby Hinsliff