The forced resignation of Britain’s ambassador to Washington is not only a national humiliation but a grim herald of the cold, capricious world that awaits the country after Brexit. Donald Trump’s thin-skinned response to Kim Darroch’s leaked criticism of his administration made life uncomfortable for the ambassador.

But it was Boris Johnson’s failure to stand up for him in Tuesday’s Conservative leadership debate that made Darroch’s position untenable. It was a clear message that the likely next prime minister would remove him from his post rather than risk the displeasure of the US president.

Some close to Johnson believe he should send a political figure to Washington, or at least a highly political diplomat, to focus on the relationship with the Trump. Trump’s fickle temperament could lead him to turn against Darroch’s successor too, however, and the British ambassador must cultivate Congress, where Democrats are more powerful, as well as the White House.

For Brexiteers like Johnson, Britain’s special relationship with the US and historical links with the Anglosphere more generally are at the heart of its new global future after Brexit. But Trump’s America is a demanding and transactional partner and the president has made clear that everything from food standards to National Health Service procurement will be on the table in any future trade deal.

Bleak reality The world in which Brexit was conceived, one of global free trade and a strong transatlantic alliance, has disappeared in the years since Trump took office. Today’s is a world of increasingly managed trade and of a great power rivalry between the United States and China in which small and medium-sized countries struggle to assert themselves alone.

The controversy over Huawei’s role in Britain’s 5G network found London under pressure from Washington to shut out the Chinese telecoms company. But China’s huge role in the British economy, from the nuclear industry to the City, gives Beijing powerful leverage too.