Spare little pity for Kim Darroch, Britain’s outgoing ambassador to the US. He leaves Washington with plaudits from fellow diplomats and will enjoy life after the Foreign Office. It is rare that someone whose career has been terminated so abruptly emerges with an improved reputation. The same cannot be said for Britain. Donald Trump’s tweeted decapitation of Sir Kim has already warped Boris Johnson’s impending government — assuming he wins the Conservative party leadership contest. It was one thing for Mr Trump to have Hungary’s Viktor Orban and Italy’s Matteo Salvini in his corner. It will be quite another to be joined by Britain’s prime minister before the end of the month.

The contrast with the start of Mr Trump’s presidency is remarkable. He began as a lonely figure among western leaders. There was talk of Germany’s Angela Merkel leading the new moral superpower. A few months later, France’s Emmanuel Macron joined her on the podium. Even Theresa May, now Britain’s outgoing prime minister, offered an implicit rebuke to the US president.

The one element of British politics that remained immune to populist depredations was foreign policy. In the past three years, the UK has stuck closely with its European partners on climate change, the Iran nuclear deal, a two-state solution in Israel and support for a rules-based international order. All that may be about to change.