Our fight, it is no exaggeration to say, is the civilized world’s fight. It is a fight for reason and comity in the affairs of nations, against an administration whose worldview, and behaviour, is increasingly that of an aggressive dictatorship, in all its crudeness and its thuggery.

Mr. Trump, as the Prime Minister has said, aims to “break us,” a phrase with historic echoes. He has to now, or others will follow our lead. If he succeeds, then the world will be governed by nothing but force in the end, in trade as in other matters. But if we prevail, then “broad and sunlit uplands” must surely await.