At moments of great crisis, national leaders and governments generally put their countries’ (and their own) interests first. Transnational geopolitical, economic and security alliances are all very well. But if such organisations do not or cannot rise to the urgent challenges of the day, they risk being bypassed, ignored or shunted aside. This is the predicament now facing the European Union.

After Donald Trump’s appalling treatment of Volodymyr Zelenskyy in full view of the watching world on Friday night, all agree that the US president’s betrayal of Ukraine, sickening embrace of Russia and his blunt demand that Europe henceforth defend itself represent just such an extraordinary challenge, and one that must be swiftly addressed.

Three developments stand out. One is that Europe’s national leaders are taking charge of crisis management, pushing the EU Commission and, to a lesser degree, US-led Nato to one side.

A second phenomenon is the Trump administration’s unprecedented hostility to the EU as an institution. Trump says the EU was created to “screw” the US – a bizarre claim even by his semi-deranged standards. Now he is threatening 25% tariffs on EU imports. He is determined to exclude Brussels from talks on Ukraine. Yet he insists Europe must guarantee any future peace.

The third, linked, development is the way Britain is unexpectedly being drawn back into the centre of European affairs after nearly a decade of self-imposed estrangement. The need to repair the dangerous folly of Brexit has never been so glaringly obvious. At the same time, Trump wants to use the UK not as a bridge, as Keir Starmer would like, but as a wedge to weaken and divide Europe.

Among national leaders, Emmanuel Macron, France’s president, is in the van. After Trump’s volte-face, he convened an emergency summit in Paris. Then he hot-footed it last week to the White House, where he spoke for Europe in seeking a continuation of US security guarantees, not only for Ukraine but for the continent as a whole.

Friedrich Merz, Germany’s chancellor-elect, is busy urging fellow leaders to “strengthen Europe as quickly as possible, so that we achieve independence from the US”. He doubts Nato’s usefulness “in its current form”. Donald Tusk is also taking a prominent role – as Poland’s prime minister, not as the holder of the EU’s rotating presidency. Capitulation to Putin is unacceptable, he says, rebuking Trump. He wants others to match Poland’s above-average defence spending.

Where is the EU in this fast-moving crisis? Plodding slowly along. The presence of Ursula von der Leyen, European Commission president, in Kyiv for last week’s anniversary of Russia’s invasion was largely symbolic. She and the other top Brussels luminary, António Costa, have been ghosted by Trump & co. It appears that no one in Washington sees any need to talk to the EU about Ukraine or anything else.

Kaja Kallas, the EU’s foreign policy chief, is trying her best. She flew to the US last week, having finally secured an audience with the US secretary of state, Marco Rubio. While she was in the air, Rubio cancelled the meeting. It was a deeply offensive, calculated snub, intended to convey contempt for all things EU.

Von der Leyen is scrambling to insert Brussels back into a debate that is passing it by. Another “emergency” EU summit is due this week, where a €20bn Ukraine aid package will be discussed. But as usual, consensus is lacking. Italy, Spain and Portugal are reportedly not keen. And pro-Putin Hungary may play its customary spoiler role, after trying to veto the EU’s latest round of Russia sanctions.

Important decisions may be put off again, to 19 March, when yet another summit will discuss pooled defence manufacturing, procurement and financing. The fact that an agreed plan to meet Trump’s challenge may prove elusive even then illustrates the bigger problem: in a crisis, the 27-country EU is not nimble enough, too easily paralysed. The need for majority voting on key foreign and security issues and curbs on national vetoes grows urgent.

This crisis will not wait. In the meantime, the onus is on national governments and mooted “coalitions of the willing” to keep Ukraine in the fight and prevent a Trump-Putin carve-up. And this is where Britain comes in. Starmer is coordinating closely with Macron on a “reassurance force” for Ukraine. And he is holding his own European leaders’ summit in London to brief them on his talks with Trump.

The wider political significance of a central UK role in boosting and re-organising Europe’s post-Trump defence, outside the confines and constraints of the EU, is plain. Closer cooperation on security and intelligence could in time generate goodwill – and consequently, more non-EU, ad hoc government-to-government cooperation on UK-Europe trade, borders, free movement and other noisome Brexit hangovers.

Nato is another multilateral organisation adrift in a world turned upside down. Ukraine aside, Trump’s defence secretary, Pete Hegseth, hints at big cuts in US troops in Europe. Does Nato’s article 5 all-for-one guarantee still hold? Would Trump fight if, say, Poland were attacked? Has the US nuclear umbrella, Nato’s last resort, folded? These are genuine questions, unthinkable only months ago.

Nato is traditionally led by a US general. But why have the Americans involved at all? Thirty of Nato’s 32 members are European. It would certainly cost a bomb, but an alliance liberated from Trump could eventually produce the “army of Europe” that Ukraine and leaders like Macron talk about. It could deter Russia. And the US, if need be.

At a moment in history when autocratic hyper-nationalists are trying to divvy up the world, multilateral organisations such as the EU, the African Union and the Arab League are more vital than ever. But not if they don’t work. Many, including major UN agencies and the security council itself, need a wake-up call. Desperate times demand bold new thinking. The choice is clear: shape up – or be trumped.