Until recently most of the world yearned for the US to become a more normal country. It had seen enough of George W Bush’s freedom agenda to put it off American exceptionalism for good. People should be careful what they wish for. Donald Trump may be the most gaffe-prone — and offensive — US presidential nominee in history. But he is also the first to scorn the belief that America’s mission should be to uphold universal values. It is not clear he even thinks such values exist. Hillary Clinton, on the other hand, is their unabashed cheerleader. “I believe with all my heart that America is an exceptional country,” she said in June. “We are still, in Lincoln’s words, the last best hope of earth.”

Long-suffering US realists — those who argue that America should merely pursue its national interests — must wonder what they did to deserve such a champion. Mr Trump vows to avoid foreign entanglements, such as pre-emptive wars in Iraq. That is what realists want to hear. Ditto for Mr Trump’s view that America’s allies should pay for more of their defence, or that China is entitled to occupy atolls in a sea named after it. Why should America always play the referee? But Mr Trump inevitably spoils things by adding his own gloss — promising a nuclear attack on Isis, for example, or claiming that President Barack Obama founded the terrorist group. The key to successful realism is tactical guile and deep knowledge of the world. Mr Trump epitomises the opposite. With friends like Mr Trump, realists need no enemies.

There is also the likelihood that he will lose to Mrs Clinton in November. Mr Trump’s defeat would probably come in spite of his foreign policy instincts, rather than because of them. For years, the US public has said it is tired of military adventures, thinks Nato allies should shoulder more of the burden and that America’s global role should be more modest. Nation-building is no longer an election winner, if it ever was one. Mr Trump’s “America first” slogan might have unfortunate antecedents (it was picked up by Fascist sympathisers in the early 1940s), but many Americans are happy with its current meaning. If he loses it will be because of his manifestly unpresidential temperament and a tendency to insult almost every group in America.