When an American president visits Britain, it is time to be reminded of two contrasting principles of foreign policy. Lord Ismay, once secretary general of Nato, summarised the aims of British diplomacy as being to “keep the Russians out, the Americans in, and the Germans down”. George Washington, in his departing speech to Congress, warned of the danger of foreign entanglements, saying: “The great rule of conduct for us in regard to foreign nations is in extending our commercial relations, to have with them as little political connection as possible.”

The latter is advice President Donald Trump seemed to be following this week. His visit has been a helpful reminder that his priority is “America First”, and that his endorsement of Boris Johnson as the next leader of the Conservative Party and his brandishing of the prospect of a “phenomenal trade deal” with Britain were designed exclusively with American interests in mind. Once Britain has freed itself of the “shackles” of the EU, Mr Trump envisages rich pickings for American businesses. A chief impediment would be the rival predations of the Chinese; and their greatest asset a prime minister on close terms with the White House with no real friends left in Europe.