In the words of Mike Tyson: “Everyone has a plan till they get punched in the mouth.” For more than 70 years, Europe has had a plan. It was to hold together against Russia and rely on the alliance with the United States. Now Europe has been punched in the mouth by Donald Trump. Europeans must therefore ask themselves the question: has Trump’s US become a hostile power? If the answer to that question is yes, the consequences for Europe – and for Britain – would be enormous. That’s why so many policymakers and politicians prefer not to ask it.

But as Der Spiegel put it last month: “The west as we once knew it no longer exists.” Even the Washington-based German Marshall Fund, a bastion of postwar Atlanticism, now talks about Trump’s “overt hostility”. Incredible as it may seem to those who grew up in a Europe and a Britain that took the US alliance for granted, the plan that has worked since the fall of Hitler can no longer be relied upon.

That recognition is not yet shared equally clearly between the European states, but it is moving that way. Europe was naturally wary of Trump at first. It placed great store on getting him to give the right reassurances, to shake hands on the right occasions, and make the right visits. But it was wasted effort and those naive days are long past – as Theresa May secretly knows better than anyone.

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The counter to this argument, still strongly made by insiders, is that the security and defence establishments remain as entwined as ever. Members of the administration, like the defence secretary, Jim Mattis and the state department’s Wess Mitchell still talk about Europe as an ally and partner. But the man in the White House doesn’t do that any longer and he won’t do so in future. For most of 2018 he has been ratcheting up the confrontation. There is no sound reason to think this is just a passing phase. The longer it continues, the more enduring its consequences are likely to be.

The Nato summit in Brussels in two weeks’ time, which Trump will attend, looms as a disaster in waiting. This is hardly a controversial prediction. After Trump walked out of the Paris climate change agreement, recognised Jerusalem as Israel’s capital, abandoned the Iran nuclear deal, declared a trade war with the EU and Canada on national security grounds and trashed the G7 summit in Quebec, it would be surprising if he says or, more importantly, does anything to reassure Nato that he regards it as anything other than a legacy arrangement in which his US has no real interest.

It is right to acknowledge that there is much that needs to change about Nato. That argument predates Trump. Both the Bush and Obama administrations rightly warned Europe that it needed to spend more on the alliance, as does Trump – as his letters to Nato members reveal.. They understandably signalled a post-cold war turn from the Atlantic towards the Pacific, and the rising power of China. Trump is doing that too. But neither Bush nor Obama called Nato or the EU into question; neither of them hymned European nationalist leaders and movements and their anti-migrant policies; and neither constantly curried special favour with Russia’s Vladimir Putin.

In reality, most European members of Nato are spending more on defence than in the recent past. Most have increased spending as a share of GDP since 2014, and in economically difficult times. Moreover, nine EU member states – Britain among them – have also agreed to establish a European rapid deployment military force, outside Nato but complementing it. In the light of Trump’s hostility, this can be seen as a significant pointer to a more autonomous European defence commitment in the future.

Facebook Twitter Pinterest ‘John Bolton’s itinerary has been equally revealing.’ Photograph: Kommersant Photo Agency/REX/Shutterstock

Trump isn’t exactly concealing his views about Europe. On Wednesday his neocon national security adviser, John Bolton, was at the Kremlin fixing a Trump-Putin summit during next month’s trip. After the Nato summit and his brief visit to Britain, it is likely that the US president will head, probably to Helsinki, for a summit with Putin, and then perhaps attend the World Cup final with him in Moscow the following afternoon. That would be a clear statement of where Trump’s priorities lie. In the light of Russia’s repeated attempts to disrupt European countries, that rapprochement would be a dagger to the heart of European liberal democracy, which ultimately only European liberal democracies can solve.

Bolton’s itinerary has been equally revealing. Between visits to London and Moscow, Bolton spent a day in Rome, where his meetings included one with Matteo Salvini, leader of the Lega and Italy’s new interior minister. That’s another clear message. Italy’s new rightwing government and its most controversial and Trumpian leader is worth talking to. Europe’s traditional leaders – Germany and France – are not.

That all this has happened in the same week in which Javier Solana, the former Nato secretary general and former EU foreign policy chief, was refused entry to the US because of a past visit to Iran, sends an uncomfortable but unmissable signal.

Twenty years ago, visiting Washington and at the height of his influence, Tony Blair made a speech that praised the transatlantic alliance in the same biblical terms that Franklin Roosevelt’s emissary Harry Hopkins had used to Winston Churchill in 1941. “Whither thou goest I will go, and whither thou lodgest I will lodge. Thy people shall be my people, and thy God my God,” said Hopkins. In a very different speech at Chatham House on Wednesday, Blair warned that Trump was bringing about the collapse of that very alliance. Blair is right about that. Times have changed, perhaps utterly, and it would be reckless of any European government, Britain’s included, to pretend otherwise.

• Martin Kettle is a Guardian columnist