As countries everywhere feel emboldened to encroach on their neighbours, the dismal prospect is of an aggressive, border-shifting 19th-century world, but armed with 21st-century weapons.

America was a successful superpower because its self-interest and realpolitik were turbocharged by an avowed faith in universal values of democracy and human rights. Mr Trump believes that, far from being a unique strength in foreign affairs, that was a foolish indulgence.