In 2003 a US-led war in the Middle East fractured western unity and divided the European family. It was a trauma of historic proportions, a watershed in some ways comparable to the 1956 Suez crisis. With Donald Trump’s decision on Iran, we may be on the verge of another such moment. On the surface, things may not look as bad as they did in early 2003. At this point, US military action against Iran is a worst-case hypothesis – not a plan. No 180,000-strong force is being built up near Iranian territory. Nor are Europeans split into two camps. In this current crisis, and despite Brexit, Europeans look like they’re sticking together.

Trump’s decision is not only extraordinarily brutal, it affects a project whose origins are found in a European initiative taken in the autumn of 2003, when the UK, France and Germany sent their foreign ministers to Tehran for talks: that project was aimed at limiting and controlling Iran’s nuclear programme through peaceful means. It took 12 years of international diplomacy, in which Europe played an important role, to reach the nuclear deal that Trump has now decided to tear up.

Make no mistake, the first country ​to benefit from a breakup between the US and Europe would be authoritarian Russia

This US move amounts to an open assault on multilateralism – something that, as history has taught us, Europeans have an existential interest in protecting and upholding. Trump’s decision can only be an own goal. US credibility will be severely affected. When a German chancellor declares – as Angela Merkel has just done, for the second time in a year – that Europe can no longer rely on the United States, you know something is amiss. Many others will now ask: how can we ever again trust a country that can withdraw overnight from solemn international agreements?

Play Video 2:11 What is the Iran nuclear deal? – video

This could end badly. When Trump realises his strategy is bound to fail, he may want to resort to military force. His decision on Iran comes after a year and a half of insults, disparaging comments, and decisions that run counter to European and western interests. He cares little about Nato, and believes the US isn’t getting a fair return on its investment in European security. He has withdrawn from the Paris climate agreement, and has imposed tariffs on steel and aluminium.

Q&A Why does Donald Trump want to scrap the Iran nuclear deal? Show Hide Donald Trump’s victory in US election in November 2016 put the fate of the deal in doubt. He had promised prior to his election to “dismantle the disastrous deal with Iran”, although many believed he might instead adopt a more rigorous implementation of the agreement and tighten sanctions already in place. This could force Tehran to violate first or make the deal redundant.

In January, he reluctantly waived a raft of sanctions against Iran as required by Congress every 120 days, but said “this is a last chance” and asked “European countries to join with the United States in fixing significant flaws in the deal”. The congressional deadline Trump faces this time is on 12 May, but he tweeted on Monday that he will announce his decision by Tuesday. Trump believes the agreement is a bad deal, which falls short of addressing Iran’s regional behaviouror its missile programme. He is emboldened by a group of Iran hawks in his inner circle, such as the national security adviser, John Bolton, and the secretary of state, Mike Pompeo. Read a full explainer here

So is it time for Europe to seek a divorce from the US? Well, not quite. For several reasons, we should refrain from entering into confrontation. Europe may be the largest trade bloc in the world, but in truth it does not have the capacity to tackle 21st-century challenges on its own, and it would have even less capacity to do so if its relationship with the US came fully apart.

There is simply no alternative to a strong transatlantic partnership. There is no available spare superpower with which Europeans would share enough interests to build a new form of alliance: China and Russia offer no such thing. Besides, transatlantic flows of trade and capital stand at the heart of the global economy, and they are irreplaceable.

Another reason to maintain a partnership with the US is the magnitude of the security risks Europe faces. Islamic State might be militarily defeated, but jihadist terrorism is a generational challenge: we cannot afford to turn our backs on cooperation with the US. The trauma of terrorist attacks in Europe remains vivid.

And then there is Vladimir Putin’s Russia, a regime challenging our continent’s security and actively seeking, through various means, to weaken and divide Europe and the west. Make no mistake, the first country to benefit from a breakup between the US and Europe is authoritarian Russia.

Certainly, US-Europe relations are now entering troubled, uncharted waters. But this could be a phase. Trump will be there for another three or seven years. But by historical standards, that’s a short period of time. The US is a vibrant and innovative economy with a dynamic, multicultural population, and is an optimistic society that cherishes individual freedom. That won’t go away. We need to think about the future.

Facebook Twitter Pinterest Protesters in Tehran react to the US withdrawal from the nuclear deal. Photograph: UPI/Barcroft Images

For us Europeans, today’s choices are difficult and there are real dilemmas. Building European unity is the first imperative. Some member states of the EU – especially in the central and eastern parts of the continent– may perhaps be tempted to give a nod to President Trump for tactical purposes – as a downpayment for US security protection. But that would be a miscalculation, as European discord would benefit only Russia.

We need to be firm with Washington. The nuclear deal, or what remains of it, needs to be supported. If it collapses entirely, that should not be because of us. Trump has taken an extraordinary gamble, and we in Europe would be the first, outside the Middle East, to suffer the consequences if yet more chaos and war erupts. Our least bad option is to show we’re ready to do what we can to preserve the 2015 deal. We need to mitigate the impact of US sanctions on European business.

Europe must make Trump pay for wrecking the Iran nuclear deal | Simon Tisdall Read more

Our limitations are, however, rather obvious. Europe can’t afford a transatlantic trade war. Its companies and banks do much more business on the other side of the Atlantic than they will ever do with Iran. If anything, this crisis should bolster calls to build up Europe’s defence capabilities. We should think of that ambition as a win-win proposition: as both a way of dispelling US statements saying we refuse to carry our share of the security burden, and as insurance that protects us against further erratic behaviour from Washington.

Since 1945 the transatlantic relationship has been the bedrock of Europe’s economy and its security. One should tread carefully with that legacy. No other US president has ever been as antagonistic towards Europe and towards the principles it defends. The American people elected Trump as president, so we have to respect that. But what we don’t have to respect are the decisions he takes that have negative consequences for everyone, ourselves included.

In 2003 my country, France, staunchly opposed the Iraq war , alongside Germany – but they were entirely unable to prevent it. Now Europeans have to find a way to mitigate the destructiveness coming out of the White House; but we must also be clear-eyed about what our capacities truly are.

• Bruno Tertrais is deputy director of the French thinktank Fondation pour la recherche stratégique