Here is a measure of America’s democratic quandary: most of the world is banking on the country’s generals to restrain its commander-in-chief. It is usually the other way round.

When asked whom they trusted to “deal with North Korea responsibly”, more than 70 per cent of Americans said the US military. Just 37 per cent opted for Donald Trump, their elected civilian president. We have not seen this movie before. When we look to uniforms to protect the world’s greatest constitutional republic from itself, something is amiss.

Yet it is where most people’s hopes now lie. In the past few days, Mr Trump has shredded America’s longstanding — and intuitive — doctrine of nuclear deterrence. Its key tenet is that the US will retaliate overwhelmingly to any attack on itself or its allies by a nuclear adversary — in this case by North Korea on the US, or on its main regional partners, Japan and South Korea. The doctrine of mutually assured destruction was understood by a succession of Soviet autocrats during the cold war. Until now, Washington’s public stance was that deterrence would also work on Kim Jong Un, North Korea’s dictator.