LONDON — Britons love a dollop of nostalgia. And there’s nothing more likely to make its politicians more wistful than the long shadow of wartime hero Sir Winston Churchill.

In 1946, it was Churchill who gave a speech in Fulton, Missouri, to declare that the United States and Great Britain had a “special relationship” that was essential for keeping the global peace.

Some 73 years later, Donald Trump has begun his UK State Visit in customary style, launching a Twitter tirade at London Mayor Sadiq Khan just minutes before Air Force One touched down.

He’d earlier praised Theresa May’s political rival Boris Johnson in a pre-trip interview, in which he also called the Duchess of Sussex “nasty” and claimed outgoing Prime Minister May had bungled Brexit.

The rocky opening was enough for the Washington Post Editorial Board on Monday to describe the visit as “a low moment” for the “special relationship,” that “will serve to put on display the widening cracks” that Trump “has introduced into one of America’s closest alliances.

Yet, as Trump holds meetings with senior UK politicians on Tuesday, many on the British side of the Atlantic are already wondering whether it is now time for a conscious uncoupling.

Just at the time when Brexit is set to make the UK more dependent on the United States, and less close to the European Union, Trump’s ‘America First’ approach to trade and diplomacy has little room for sentiment, even for an old ally.

Normally, when a country hosts the leader of a friendly nation, big joint investment deals are arranged in advance, PR gifts ready to be unwrapped by the politicians.

This time, there are no plans for a major announcement of US and UK companies delivering fresh contracts or jobs. Business chiefs will gather in Downing Street, but the twin threats of a global trade war with China and of a ‘no-deal’ Brexit make many in commerce nervous.

As Trump refuses to listen to London about the urgency of tackling climate change, or sticking with the Iran nuclear proliferation deal, this always unbalanced partnership feels more than ever like an unrequited love affair.

It’s true that in some areas, the president has been influenced by May on issues, such as sending home Russian spies after the poisoning incident that killed two British nationals.

And he’s been more than grateful for British support for his constant plea for NATO countries to spend more on their own defence budgets, rather than relying on America’s troops and cash.

ASSOCIATED PRESS Prime Minister Theresa May and her husband Philip greet Donald Trump and first lady Melania outside 10 Downing Street in central London, Tuesday, June 4, 2019. May and Trump didn't shake hands during the meeting.

Away from the soaring rhetoric about a shared language and values, the UK and US’s close ties really stem from their military and intelligence links. What May calls “our longest and deepest defence and security relationship” is cemented daily through the two countries’ joint working of their armed forces and intelligence agencies.

We have a common pool of Trident nuclear missiles and nuclear reactors for warships and submarines. Britain is the second largest operator of America’s new F35 fast jet programme, locking the UK into a system that is designed for the next 40 years. Our troops and airmen work closely round the clock in Iraq, Syria and Afghanistan, as do our spies, cyber warfare specialists and special forces.

But on Putin and on foreign policy more broadly, many British diplomats fear that Trump simply lacks his predecessors’ suspicions about Moscow and its power plays in Crimea, the Middle East and across Europe.

Sir Peter Ricketts, Britain’s former National Security Adviser, says Trump’s rise has prompted a rethink in just which areas the two countries’ interests now coincide.

“I’m struck that over the last couple of years the UK-US relationship has become more segmented. By that I mean that in areas like defence it is as special as ever. Indeed the drive by Macron and Merkel to use Brexit to move towards a European army is pushing Britain further towards the US and NATO,” he says.

“But in other areas - the Iran nuclear deal, trade policy, carbon reduction, handling Putin - we find ourselves much closer to the European approach than Washington’s. I don’t see anything alarming in that.

“As the centre of gravity in US foreign policy moves to competition with China, it’s inevitable that they will have different interests and priorities from us in some areas. That doesn’t prevent us having a really strong partnership where our interests coincide.”

Former US Secretary of State Dean Ascherson was the man who came up with a more hard-headed assessment of Britain’s waning powers. It had “lost an empire, but not yet found a role”, he said in a speech at West Point in 1962 - just 16 years after Churchill’s love letter to America.

In the 1970s, the UK found Europe as its new anchor economically and politically, but those bonds are looser than ever and soon to be cut entirely once Brexit actually happens.

It was another US Secretary of State, Henry Kissinger, borrowed from former British Prime Minister Lord Palmerston, that “America has no permanent friends or enemies, only interests”.

Under Barack Obama, those interests looked increasingly across the Pacific, not just the Atlantic. And even among European leaders, London looked second best.

“In some areas - the Iran nuclear deal, trade policy, carbon reduction, handling Putin - we find ourselves much closer to the European approach than Washington’s. I don’t see anything alarming in that.” Sir Peter Ricketts, former UK National Security Adviser

In a line that wounded both May’s predecessor David Cameron and British pride, at the end of his term Obama said it was German Chancellor Angela Merkel who “has probably been my closest international partner these last eight years”. Proof that even before Trump, this old alliance was perhaps on borrowed time.

Early in his presidency, Trump turned to French President Emmanuel Macron to provide a more macho bond than either Merkel or May could offer. That brief dalliance cooled when Macron realised Trump would never give up his opposition to the Paris climate change accord, his scepticism about Nato and his desire to tear up the Iran nuclear deal.

May is a lame duck leader, now that she has announced she will stand down next month. And the prospect of a new British prime minister is making Trump turn to the UK once more, at least rhetorically. He and Boris Johnson would certainly have more in common than other world leaders. Johnson and Trump had a “friendly and productive” 20-minute phone call but the former foreign secretary turned down the offer of a face-to-face meeting, the Press Association reported on Tuesday.

It’s true that on a political level, the “special relationship” relies on a personal chemistry between the occupants of the White House and Downing Street, as well as sensitivities about the fact that the US is clearly the dominant partner.

Churchill and Roosevelt forged their friendship in the Second World War and early Cold War, Macmillan and Kennedy overcame political differences, Thatcher and Reagan literally danced together on a trip to Washington.

Blair and Bush were perhaps the closest president and prime minister in recent years. I remember being among the press pack at Camp David in 2001 when George W Bush revealed to a stunned press corps that he and Tony Blair used the same Colgate toothpaste. Blair quipped: “They are going to wonder how you know that, George.”

ASSOCIATED PRESS George W Bush and Tony Blair at Camp David in 2001.

That was before the Twin Towers attack, and everything that followed, but many Britons still cringe at Blair’s approach. The perils of getting too up close and personal with a President were summed up by a now infamous memo written ahead of the Iraq war, in which Blair said ‘I will be with you, whatever’.

Johnson, who once ridiculed Blair’s neediness in relation to Bush, looks like he’s already signed up to the Trump cause. Flattery may well work in some small way, yet the rifts over Iran and over Chinese telecoms giant Huawei prove that supreme national self-interest is what matters most to the White House.

Unusually, Trump has even hinted that the one usually inviolable bit of the ‘special relationship’ - intelligence links between the CIA and UK counterparts - could be ended if the UK insists on giving Huawei some access to its 5G phone network.

Things could get worse still. If the Labour Party’s Jeremy Corbyn becomes prime minister, the UK will have in Downing Street the biggest critic of American global power that it has ever seen. And thanks to Trump, Corbyn’s scepticism is no longer the preserve of the radical Left in Britain.