The cruellest remark made about Britain by an American came out of the mouth of Dean Acheson, secretary of state to President Truman. Speaking in the early 1960s, he bagged himself an immortal place in the books of quotations with the withering observation: “Great Britain has lost an empire and has not yet found a role.”

The first half of that sentence was obviously correct. At its zenith, the British empire held sway over a quarter of the land surface of the planet. Quite a feat for a modestly sized, wet and blowy island in the north-east Atlantic. This was an empire over which “the sun never set”. Until it did. By the time Acheson delivered his jibe, there were only a few pink specks under the continuing rule of Britannia. It lingered also in some lines in the national anthem, the archaic handles on honours and a residual belief, sustained by Britain’s heroism in the Second World War, that there remained something exceptional about these islands.

This dramatic change in their country’s place in the world required a lot of psychological adjustment by both the people and the governing classes of Britain. Among some there was acute post-imperial angst, which still lurks in the current debates about our place in the world. But contemplated from a long perspective, Britain handled the reduction of its global status really quite well. Acheson was proved wrong. Britain did locate a role; in fact, it created more than one role, each being enhanced by interlocking with the other. One flowed from Britain’s close attachment to the superpower that replaced it, the US. Sensible people avoid that cloying cliche, “the special relationship”: one of our ambassadors to Washington even banned his staff from using it for fear that it inflated British estimations about how important this country is in the eyes of Washington.

It is nevertheless true that the alliance with the US gave Britain enhanced leverage in the world. This relationship has survived periods of distance between the two countries, such as Harold Wilson’s shrewd refusal to send British troops to join the Vietnam war. It has endured disasters of over-proximity, the most notable recent example being the invasion of Iraq. In the Opinium poll that we publish today, and notwithstanding the agreement of the majority that Donald Trump is a dangerous president, half of the respondents selected America as our most important ally.

The other key relationship has been with the European Union. Though that has always been riddled with ambiguities and tensions, the EU’s development was crucially influenced by Britain, often in ways its leaders and people never properly acknowledged to themselves. Membership of the EU enhanced Britain’s value to America as an ally; Britain’s ties to the United States gave the British additional traction within Europe.

Together, these alliances placed Britain at the centre of all the major international agreements and institutions that have underpinned peace, security and prosperity in what we once called the west. I don’t care for the phrase “punching above our weight”, but that cliche beloved of some Foreign Office mandarins had a kernel of truth. By being both a close ally of the United States and a major actor in the EU, Britain created a privileged space for itself in the world.

All of this, the product of decades of nurturing influence and building alliances, is now in jeopardy. Contrary to those who suggested that he would be sedated by office, Donald Trump is governing in the same way that he campaigned. His frenzied first 15 days in power demonstrate that he is the belligerent, nationalist, protectionist that he said he would be. This is not the first time that America has produced a president who horrifies many Britons and impels some of them on to the streets in protest. Ronald Reagan did that and, in more recent memory, so did George W Bush. But it is a category error to place Mr Trump in the same bracket. Never before has the occupant of the White House been so potentially lethal to the international norms and the complex matrix of global agreements that have been so vital to Britain’s security and prosperity.

And just at the very moment that Britain is tearing up its alliance with its closest neighbours. This is not the only time that Britain’s relations with the EU have been turbulent, but it is the first that we are actually going to file for divorce. At the same time, and making Britain’s dilemmas even more acute, the two key global actors that we have depended on for so long are now in a state of escalating hostility towards each other.

Pimping out the Queen for Donald Trump. This, apparently, is what they meant by getting our sovereignty back

When the EU’s leaders met in Malta on Friday, much of their summit became devoted to how they ought to respond to the Trump ascendancy. Mrs May joined them in the wake of her hand-holding at the White House. Straining for any leverage she can locate to help her forthcoming negotiations with the EU, and hoping to impress her fellow leaders that she can still be useful to them, the prime minister promised that a post-Brexit Britain would continue to be “a valuable partner”. As a token of which she offered herself as a “bridge” across the Atlantic. This is what British prime ministers have traditionally done at times of transatlantic stress and sometimes with success. But that playbook has been shredded. Her offer to be a go-between was met with a rebuff. The wittiest of the responses came from Dalia Grybauskaitė, the president of Lithuania. There was, she said, no “necessity for a bridge” when they could all communicate with the American president via Twitter.

Even if Europe is looking for a bridge-builder to the Trump presidency, it would be unlikely to outsource that task to Britain, a country that is torching its own bridges with Europe. As for Mr Trump, it is not bridges but walls that are his preferred kind of construction project. He scorns the EU and gleefully expresses the hope that it will fall apart.

This is one of the many reasons why Mrs May ought to be highly wary of how far she is willing to go to achieve intimacy with the new occupant of the White House. I have heard very senior officials in the British government describe her recent trip to Washington as “looking desperate” and “needy”. In response to that criticism, her allies say that you have to play the cards you are dealt and you don’t get to choose which leaders other countries put around the table. Mr Trump cannot be simply ignored. He is now the most powerful man on the planet. When asked what tangibles the prime minister extracted from her visit, they argue that she moved him from his previous view that Nato is “obsolete”. It is notable, though, that the claim that he is now “100% committed” to Nato were words the prime minister put into his mouth, not ones he uttered himself.

Her allies were delighted that the president compared their relationship to Ronald Reagan’s bond with Margaret Thatcher, rather than seeing that as the self-serving flannel of a serial fabulist. In a host of key areas – relations with Russia, Iran, climate change and free trade – his postures are antithetical to Britain’s positions and interest.

Some ministers mutter that the big mistake was to issue the invitation to make an early state visit to Britain, a notion conceived as a way of flattering his colossal vanities. At the very least, it would have been prudent to wait before rolling the royal red carpet. Pimping out the Queen for Donald Trump. This, apparently, is what they meant by getting our sovereignty back.

The visit is already giving nightmares to those who will have to arrange it. Buckingham Palace is known to be cross that Mrs May issued the invitation at a news conference and is not amused by the prospect of the Queen being forced to share the state coach and other confined spaces with Donald Trump. Those who will be tasked with the security fear that it will attract massive protests, potentially greater than ever before witnessed when a foreign leader has visited these shores.

You can argue that Theresa May, our somewhat accidental prime minister, is a victim of her baleful circumstances. She just happens to have ended up in charge when the music suddenly stopped. She did not campaign for Brexit, even if she did not do an awful lot to campaign against it either. She would not have chosen to be dealing with President Trump. Though she would never be so incautious as to be heard saying so, I have absolutely no doubt that she would have voted for Hillary Clinton. The deep forces that have stranded Britain in such a precariously lonely place are also much bigger than one mere prime minister.

What is her responsibility is how she navigates these unprecedented times. If President Trump proves to be as calamitous as he is threatening to be, she will pay for taking too short a spoon when she supped with him. If Brexit goes horribly wrong, a lot of the people who voted for it will conveniently forget what they did in the referendum and blame her. As another, and rather better, US president once said about leadership: the buck stops here.

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