With a mixture of regret, laced with incredulity, European leaders gathered in Brussels to marshal their forces for a power struggle not with Russia, but with the US.

Even now, of course at the 11th hour, most of Europe hopes this coming battle of wills can be averted and the Trump administration can still be persuaded that forcing Ukraine to the negotiating table, disarmed and blinded, will not be the US’s long-term strategic interest.

It has fallen to John Healey, the UK defence secretary; and Tony Radakin, the chief of the defence staff, meeting their opposite numbers in Washington to see if there are any conditions in which the US will provide the backstop Europe insists it needs to send a reassurance force into Ukraine to protect a ceasefire. One European diplomat said: “We will know very soon if the US has set its face against helping Europe, and what its explanation is.”

As the French president, Emmanuel Macron, put it in his patriotic address on Wednesday night: “I want to believe that the United States will remain at our side. But we must be ready if that is not the case.” In saying this, he caught the spirit of the Brussels summit, and the new mood in Germany being led by the chancellor-elect, Friedrich Merz.

It is, so far as relations with Washington are concerned, a mood of optimism of the will combined with pessimism of the intellect. It requires Europe to prepare for a severance with the US, and one that may come much sooner than Nato planners had envisaged.

Specifically, it requires European nations to upend their economies and throw out their fiscal debt rules that once seemed immutable, even if it risks a confrontation with the bond markets as well as part of their electorates. “Whatever it takes,” the slogan coined by Mario Draghi, the former head of the European Central Bank, to get Europe through the eurozone crisis, is being revived to get Europe through this security crisis.

But in a sense, diplomats say, as with the eurozone crisis this is not just about money, or even transferring resources to spend more on defence over the next four years, critical as this will be. This is about political will, and taking the mental leap of independence from America. One western diplomat said: “Macron was probably right in his talk of European strategic autonomy. We have wasted seven years not building a European defence capability, and now we must make up for lost time.”

The first stage is to put Donald Trump on the back foot by showing that Ukraine is not the war party, as claimed by the US vice-president, JD Vance. Kyiv’s proposal for an immediate pause in the fighting covering sea, air and energy installations is backed by Macron and the British prime minister, Keir Starmer. The aim is to flush Vladimir Putin out and try to show the White House that the obstruction to a ceasefire and a just deal lies in Moscow and not Ukraine.

One European diplomat said: “With Trump only putting pressure on Ukraine to negotiate, no questions have been asked of Putin’s terms for a deal, and no pressure has been applied on him by the White House. It is outrageous.”

The second stage is to consider what Europe, probably allied with Turkey, Canada and even Australia, can do to help Ukraine if the US refuses to provide the backstop, or to end the pause on its supply of weapons to Ukraine. Can Europe self-assemble a short-term package of ammunition, weaponry and intelligence that acts as a substitute for what the US supplied and at least buys Volodymyr Zelenskyy some time? European countries insist they can send to Ukraine this year at least 1.5m rounds of artillery ammunition, air defence systems and missiles, drones and other equipment.

An additional proposal is to challenge Trump to sell to Europe the arms he is refusing to supply to Ukraine. If Washington rejected such a highly commercial offer it would reveal that Trump’s concern was not the cost to the American budget of helping Ukraine, but something more geo-strategic. The seizure of Russian central bank assets to fund this has not yet been ruled out, diplomats say, but will be discussed later.

But either way, it is the speed of irreversible events, notably in Germany as much as Brussels, that have diplomats on the back foot.

German concerns about debt, born of historical fears around Weimar-era inflation, are being hurled out the window. Merz’s Christian Democratic Union campaigned right up to election day on a promise to make budget savings while Olaf Scholz insisted lifting the restrictive debt brake rules in the German constitution was unavoidable. The SPD badly lost the election, but triumphantly won on the policy when Merz did a post-election volte face.

In a bid to push the extra spending through, and knowing they lack the required two-thirds majority to change the debt rule in the newly elected Bundestag, the SPD and CDU are rushing the change through the outgoing Bundestag elected in 2021.

It is a head spinning change. It is also deeply ironic that an election triggered largely by a coalition dispute about spending an extra €8bn-€9bn (£6.7bn-£7.5bn) has ended with an agreement to set up an off-the-books €100bn infrastructure fund over 10 years. Moreover, this is all being proposed by Merz, the most staunch Atlanticist in the CDU.

But Germany now openly questions where Trump’s loyalties lie, and even if he will be seen in Red Square on 9 May alongside Putin on the 80th anniversary of the end of the second world war.

Indeed it is unlikely Merz would disagree with the Ukrainian ambassador to London, Valerii Zaluzhnyi, who told a Chatham House conference: “We see that it is not only Russia and the axis of evil trying to destroy the world order, but the US is actually destroying it completely.”

The Ukrainian envoy, a former commander-in-chief of the Ukrainian armed forces, added that talks between the US and Russia – the latter of which was “headed by a war criminal” in Putin – showed the White House was making “steps towards the Kremlin regime, fully realising that in this case Europe could be a new target for Russia”.