Now comes the paradox. Trump sits in a White House war room, preaching the same “national security” he derides in Syria to justify his $5bn Mexican wall. Migration involves appalling suffering, on which Britain has no right to be smug. Britain has Shakespeare’s “silver sea, which serves it in the office of a wall”, where a few patrol boats will apparently suffice. But the issue is the same – how to honour populist election pledges to keep out migrants.

Trump is entitled to put “America first” in the Middle East, and that slogan may explain his trade barriers against Canada and China. But like the Mexican wall, such policies have nothing to do with America’s national security. The US must be the safest country on the planet. Its home territory has never been so much as menaced by a foreign power, let alone invaded. Two oceans protect it east and west. 9/11 aside, terrorist incidents have been homegrown. Wars abroad, from Vietnam to Syria, have reflected some neo‑imperial hegemonic urge, similar to that which used to grip Britain. The effect has been to turn the US from policeman to random vigilante.

The politics of fear has long been the default mode of the insecure statesman. The parading of military muscle still permeates the US’s public realm and has become a shop window for what President Eisenhower termed the anti-democratic “military-industrial complex”. Its endless aggrandisement boosts military spending and upholds the cause of an American presence across the globe. It worships daily at the altar of national security.