Donald Trump’s tearing up of the special relationship with Britain, in just one tweet, was unquestionably a watershed. But in the process the United States president may unwittingly have cast the UK’s relationship with Europe in an entirely new light.

A few weeks before Trump fired off the tweets spreading neo-Nazi propaganda, and followed up with an insult to Theresa May, I met a former official of the Obama administration in Washington. The US-UK relationship, he said, “has for quite some time revolved a lot around Britain’s membership in the EU”.

“For years, we Americans have used the British as our main entry point to Europe when we wanted things done by allies,” he continued. “The British, in turn, would make the case that their input in Europe was key, which buoyed their importance. Some of this could be make-believe, but the thrust of the relationship had to a large extent come to rest on Britain’s links with Europe.”

When I asked what he thought the future would look like after Brexit, he threw his arms up in the air: “All that will be gone. In fact, it’s gone already as Britain pulls out. We just won’t have the same kind of interest in nurturing the link with Britain.”

Trump is certainly bad news for Britain. He’s bad news for any country that is democratic and wants to uphold the liberal world order rather than let it unravel into the kind of chaos that would cost everyone dear. But if this is now a tipping point, then taking a deeper look at how keeping close to Europe serves Britain’s interest surely makes sense.

Britain’s relative power in global affairs is not what it used to be. Nor can it possibly return to the era of empire. America’s commitment to the old continent is not what it once was either. What can destabilise Europe will just as surely destabilise Britain. History has already shown that to be true, but recent developments have illustrated it further: Russian aggression; China’s growing clout and geopolitical appetite; migration; new forms of terrorism; and cyberwarfare, to mention just a few.

How well can Britain deal, alone, with internet giants throwing their weight around in business and in the workings of democracy? How can it, alone, play a role in harnessing globalisation so that it benefits everyone? How can Britain, in isolation, have any sway on climate change? How can it ever, as a solitary actor, further the fight against global inequality and offshore tax evasion, or have its voice heard on human rights violations, from Syria to Myanmar?

Many of the answers to these questions lie in what Britain is now getting ready to squander – belonging to a 500 million-strong bloc: the EU.

Britain has always had a complex relationship with the postwar European project. From the 1970s onwards, its domestic politics have often been jolted by the question of how to define its place within that evolving construct. Britain opted to combine a privileged relationship with the US and the advantages it could draw from being in the European club. Margaret Thatcher’s push for a single market, and Tony Blair’s European leanings, were all part of that story. So was Labour’s choice, in the late 1980s, to adhere to the notion of “social Europe”, a combination of a market economy and social protection, in which workers’ rights and environmental norms would be protected.

The EU is an imperfect entity. But look at what the rest of the world has to offer – from China’s autocratic state capitalism to America’s blatant social inequalities and growing isolationism, not to mention the corruption and lack of rule of law found in many “emerging” countries – and surely it is obvious where Britain’s best partnership can be found.

Consider also how different Britain’s outlook might have been if it had stuck with its large European neighbours, France and Germany, rather than with the US, in the run-up to George W Bush’s Iraq war.

The EU is the antithesis of illiberalism. That’s one reason why Trump has so often lashed out against it

Obsessing about Trump is understandable, especially in a country so culturally and strategically intertwined with the US. But constantly emphasising that transatlantic dimension, even in “resistance” mode, misses the much more urgent and logical task at hand – which is, even at this late stage, to prevent Brexit from happening.

Can Trump’s miserable presidency be that wake-up call? Like many Europeans, I can only watch the UK – confused and seemingly heading towards oblivion – with a deep sense of bafflement and regret; certainly not with schadenfreude. If Trump’s America shows anything, it is that the transatlantic gap is likely to widen not just diplomatically but on values too.

The EU may be struggling with the strains of populism within its separate nations, but populism certainly isn’t what the collective project is about. In fact, the EU is the antithesis of illiberalism. That’s one reason Putin works so hard to undermine it, and why Trump has so often lashed out against it.

These days, Britain spends a massive amount of energy counting points in the divorce talks with the EU. It now needs to discuss the deeper question of where its true friends are. They are not in the White House. They are on the other side of the Channel, across a diverse continent trying to gear itself up to defend its interests in a fast-changing world.

• Natalie Nougayrède is a Guardian columnist