Remember the Taming of the Trump? When his election stunned the planet, there were quite a lot of cool voices on both sides of the Atlantic who contended that the 45th president of the United States would be tempered by power. Appearing to mistake him for a fine wine, they argued that he could be “matured”. Encumbered by the great responsibilities of the office, contained by the institutions of the United States and modulated by the American diplomatic establishment, he would evolve into a president traditional allies of the United States could handle. It wouldn’t be easy – few were foolish enough to believe that – but it would be manageable.

That view was especially prevalent in the upper reaches of the British government this time last year. While much of the world reacted to him with fear and foreboding, sanguinity flowed through the blood of much of London SW1. Whenever I expressed scepticism about this taming thesis, members of the government told me to hang on to the idea that he was a businessman. “Always remember that,” said one phlegmatist in the cabinet. “He likes to cut a deal.”

Number 10 gambled that Theresa May could keep the relationship special, even with a president as reckless as he was narcissistic, as inconstant as he was inflammatory and as contemptuous of the established norms of international diplomacy as he was of the conventional decencies of democratic politics. Mrs May made a dash across the Atlantic to call at the White House in his first week in residence. There was little in common between a prime minister brought up in an Oxfordshire rectory and Donald “grab them by the pussy” Trump. The vicar’s daughter tried to gloss it as best she could by claiming that “opposites attract”.

The ticket price for that audience was far too high. She flattered his vanities by issuing an invitation to pay a state visit to Britain, an honour accorded to very few previous presidents and never so early. “Pimping out the Queen”, as I rather rudely called it, was controversial enough when the invitation was first issued and has since become a hideous albatross around Mrs May’s neck. Another cost of supping with too short a spoon was to her dignity and her country’s reputation.

The apologists had an answer to all that. Britain has to have a relationship with the United States, whoever is in the White House. “Hug them close” has been the lodestar of British foreign policy since the Second World War. The perceived imperative to cleave tight to Washington was increased by Brexit. When Britain was separating itself from one historic partnership, it could not afford to break with the president of the United States at the same time. Yet that is happening anyway. Britain is confronted with the simultaneous fracturing of its two most important relationships, on the one side because of choices Britain has made and, on the other, because of choices America has made.

Facebook Twitter Pinterest Donald Trump retweeted posts by Jayda Fransen, the deputy leader of the British far-right fringe group Britain First. Photograph: AP

Even before the extraordinary rupture of the past few days, Anglo-American relations were in a bad way. It is true that co-operation has continued at an institutional level. I don’t doubt it when Amber Rudd, the home secretary, says that intelligence-sharing about terrorism has saved British lives. At a political level, Mrs May’s misjudged sycophancy has been reciprocated with nothing but grief. Donald Trump has torn up America’s commitment to treaties tackling climate change, a subject into which Britain has put a lot of effort under successive prime ministers since Margaret Thatcher became convinced that global warming was a threat. He has threatened to unravel the nuclear deal with Iran, another issue on which Britain has expended considerable diplomatic energy. This has been accompanied by a series of rows over trade that ought to have exploded the notion that Britain will be rewarded for leaving the EU with a generous deal from the United States.

This crisis in Anglo-American relations has been brought into sharp focus by the president’s endorsement of anti-Muslim hate videos manufactured by a far-right splinter of the racist British National party. When his retweet amplified attention for their vile output, you had to suspect that he had no, or little, idea who they were. That makes it even less excusable. Mrs May was right to call Britain First a “hateful organisation”. Saying: “It is wrong for the president to have done this” was the most diplomatic form of rebuke that she could have mustered in the circumstances. It was then a typically Trumpian choice to escalate with contemptuous personal abuse of the prime minister – after he’d first mistakenly directed the attack on a self-described “mum from Bognor” who has a similar Twitter handle to that of the prime minister. This takes us into unvisited territory. There have been plenty of rocky stretches in the Anglo-American relationship, but never before has there been such a vividly public breach between the occupants of the Oval Office and Downing Street. I cannot recall a precedent for the British ambassador in Washington formally complaining to the White House about the behaviour of the president.

Demands for him to make an apology are highly unlikely to be satisfied. He doesn’t do sorry. The Tory MP Nadhim Zahawi has sent a letter, volunteering to take Donald Trump on a guided tour of British cities to “see how our Muslim communities live peaceably alongside others, enrich their local areas and contribute so much to society”. That’s a sweet idea, but I can’t see it happening. Labour’s Paul Flynn proposes that the president should be arrested for inciting racial hatred. This will be a popular idea, but it is not a terribly realistic one. The Tory Peter Bone voices the hope that Mrs May can persuade Donald Trump to terminate his Twitter account. Good luck with that.

The only practical sanction available to Britain is to cancel the invitation to a state visit, which would win Mrs May plenty of plaudits here, at the cost of intensifying the conflict with the White House. The chances of the state visit happening were anyway receding towards zero. Number 10 does not deny that it could be delayed until 2019, which sounds like a euphemism for never. There is now also a cloud of doubt over whether a “working visit” to open the new US embassy in London in the new year will happen.

If there is anything positive to be said about all this, it is that it ought to burn away some of the residual illusions about where Britain is going to be left once it has quit the European Union. One of the arguments advanced by the Brexiters was that we could risk a detached relationship with the EU because there was always America to fall back on, a better friend anyway, in their world view. Loosed from its moorings to Europe, Britain would take to the global high seas and thrive as a member of the “Anglosphere”. Barack Obama, when he was leader of the “Anglosphere”, tried to puncture that myth. He came here during the referendum campaign to warn that a Brexit Britain could not expect any special deals on trade from the United States, which would always look to its own interests first.

This caution did not have the effect on public opinion that was hoped for by Remain campaigners, perhaps because people felt he was only saying it to try to do a favour for David Cameron. It has taken Mr Obama’s brutish successor to give a raw lesson to Britain about the realities of the so-called special relationship.

America is a very powerful country, with strong historical bonds and contemporary links with Britain, but it is not on the planet to be our patron. It has its ambitions and priorities; we have ours. Sometimes, those ambitions and priorities elide; sometimes, they are in tension. Sometimes, America will have a president most Britons will like; sometimes, it will have a president who appals most Britons, although it has never before had a president who has united MPs of all complexions in such vigorous condemnation.

I used to think Britain had handled its retreat from empire and decline from great power status as well as could be reasonably expected. Post-imperial Britain cleverly leveraged additional influence through its alliances with the United States and the EU. We gained traction with each through the relationship with the other and had more weight with the rest of the world from our connections to both. That intricate and subtle matrix, built up over decades of alliance building, has been imperilled in barely over a year. It was not Britain’s choice to have the Oval Office occupied by Donald Trump and his presidency would be a nightmare to navigate for any prime minister. It was Britain’s narrow choice to leave the EU. And it was the May government’s decision to pursue one of the harder – in all senses of the word – versions of Brexit.

This is Britain’s self-inflicted snare: to be rupturing its relationship with its traditional partners on its own continent, just as its traditional ally across the Atlantic has gone rogue.

Think of this as the latest lesson in the nation’s continuing and expensive education about how lonely life can be for a prosperous, middleweight country without reliable friends in a tempestuous world. The water in the mid-Atlantic is deep and the sea temperature is icy cold.