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 Darroch has already warped Boris Johnson’s impending government – assuming he wins the Conservative party leadership contest. It was one thing for 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 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.

Johnson will begin his job as Trump’s partial hostage. Having failed to defend Darroch, he has ceded US control over Britain’s decision-making before he enters Downing Street. He has already alienated Brussels, which leaves him one place to turn – Washington.

Nobody receives help from Trump for free. The price will be to embrace the no-deal Brexit that Johnson vows he can avoid. Without that, Trump cannot secure the US-UK trade deal that he wants. Anti-Americans used to say that Britain was its poodle. Johnson risks starting off as Trump’s lapdog.

There should be no mystery about Trump’s endgame. He has called for others to leave the EU. He refers to the bloc as a geopolitical “foe”. In contrast to Darroch, who was always polite to the Trump administration in public, Trump’s ambassadors frequently snipe at their hosts. Woody Johnson, the US ambassador in London, is an avowed no-deal Brexiter. Rick Grenell in Berlin is an open friend of the German populist right. None has been given the Darroch treatment. What Trump’s emissaries say in public is far stronger than what Darroch said in private.

Transactional world It does not follow that Trump is building a coherent alternative to what remains of the West. His goal is to bring about a transactional world in which each country fends for itself. That suits his idea of the natural order of things since America is the most powerful. The only thing that America First, Britain First, Italy First and Hungary First would have in common is dislike of the countries that still value the western alliance. Being united in disdain is very different to sharing values. This new America cannot be counted on to come to your aid in a crisis. There may be honour among thieves. There is no charity between renegades.

Two small, but significant, events this week show how rapidly things are changing. The first was a 22-strong coalition condemning China’s incarceration of 1m or more Uighurs in Xinjiang. Most of the West signed up – barring Italy, Hungary and the US. May’s UK did sign. It is questionable Johnson would have. Trump makes no pretence of caring about what happens in China. As the Financial Times reported this week, Trump told Xi Jinping he would drop US support for the Hong Kong protesters in exchange for trade concessions.

The second was the launch of a commission on “unalienable rights” – Trump’s take on which human rights he likes. Mike Pompeo, the US secretary of state, left little doubt in which direction it would go. He said rights should be based on “natural law”, which is code for opposing abortion, same-sex marriage and other rights that “have come into tension”. The intended audience was the US evangelical vote. Autocrats around the world will be the main beneficiaries.