This week, a senior German official pointed out to me that, ‘The Iran nuclear deal is the last firewall preventing military tensions in the world’s most combustible region from spilling over into thermonuclear war.’ That language is unusually apocalyptic, but it reflects a genuine fear that US President Donald Trump could soon dismantle a crucial line of defence that Germans and other Europeans are proud to have built.

European leaders have been on the back foot since January, when Trump gave them a deadline ^[1] of 12 May to ‘fix the terrible flaws of the Iran nuclear deal’, or he would re-impose sanctions on Iran. Trump’s main objections to the deal are that it does not address Iran’s misbehaviour in the region or its ballistic missile program, nor does it prevent Iran from restarting its nuclear program after 2025. And now that Trump has installed a hawkish new foreign-policy team ^[2]—with John Bolton as national security adviser and Mike Pompeo as secretary of state—European diplomats fear the worst.

Over the past few months, the German, French and British governments have been frantically assembling a package of measures—including potential sanctions on Iranian elites—to address Trump’s concerns. And both French President Emmanuel Macron and German Chancellor Angela Merkel have now visited ^[3] the White House to persuade Trump that it is better to build on the deal than blow it up.

In the short term, the Europeans are hoping that their proposed measures will allow Trump to declare victory while remaining in the deal. They have reminded Trump that a diplomatic solution to the North Korea nuclear crisis could very well depend on whether he unilaterally abandons America’s commitments to Iran under the Joint Comprehensive Plan of Action (JCPOA).

In the long term, though, European leaders’ ability to save the deal will depend on the extent to which they can act in their own interests, rather than being a hostage to the caprices of the Trump administration.

It is fitting that the Iran issue has come to the fore around the 15th anniversary ^[4] of the start of the Iraq War. For European diplomats, that disaster and the success of the JCPOA have come to represent two foreign-policy extremes. Iraq was post–Cold War Europe’s darkest hour, with European countries lined up against one another to support or oppose the war, even though none had any real influence over US decisions.

The JCPOA, by contrast, is seen as modern Europe’s shining success. Desperate to avoid another war in the Middle East, Europeans, starting in 2005, began to define their own interests in the region. With the two-pronged goal of preventing Iran from acquiring nuclear weapons and avoiding another war, they devised various carrots and sticks to shape Iranian and US actions.

To Iran, European diplomats offered a choice between two futures: one in which Iran would freeze its nuclear program and end its international isolation; and one in which it would maintain its program and face ever-harsher sanctions, and possibly war. At the same time, the Europeans, having convinced Russia and China to back their strategy, approached the US with another stark choice: either join an international coalition to apply diplomatic pressure on Iran, or pursue dubiously effective military measures on your own.

Today, European leaders’ overarching goals in the Middle East are to de-escalate the hegemonic struggle between Iran and Saudi Arabia, prevent nuclear proliferation, combat terrorism and staunch the flow of refugees into Europe. But many of these goals are now being actively undermined by the Trump administration, which has made a show of siding with Israel and Saudi Arabia against Iran in regional conflicts from Yemen and Iraq to Lebanon and Syria.

Diplomats in some EU member states have started to worry that attempts to placate Trump could force them into self-defeating positions, thus reprising the relationship between British Prime Minister Tony Blair ^[5] and US President George W. Bush in 2003. As one official confided to me, the introduction of new sanctions will make it even harder to keep Iran committed to the JCPOA, let alone engage with it on other regional issues.

Nevertheless, the European approach so far has been carefully calibrated both to win over Trump and preserve Iran’s commitment to the deal. Needless to say, this requires a delicate balance. If the Europeans give Trump too much, they will be playing into the hands of US hardliners.

At the same time, they will be empowering the hardliners in Iran. In a recent interview, political scientist Nasser Hadian ^[6] of Tehran University told me that moderate Iranian leaders such as President Hassan Rouhani ^[7] and Foreign Minister Javad Zarif have already been left in a weak position, with hardliners now saying, ‘We told you so.’ In Hadian’s view, the greatest danger is that Europe will try to appease Trump ‘at any cost’, when it should be working ‘on a plan B to save the deal without the US’.

Among other things, a plan B would offer Iran economic relief if the US were to re-impose sanctions, conditional on Iran’s continued compliance with the JCPOA; and it would provide the basis for a larger strategy of engaging with Iran and other stakeholders to de-escalate regional conflicts. Of course, it would be better for everyone if Trump agrees not to abrogate the nuclear deal. But to persuade him of that, Europe must show that it is willing to go it alone.

To that end, Trump should be confronted with a clear choice: either preserve the JCPOA, in exchange for European support in addressing regional issues and Iran’s missile program; or scrap the deal and risk the loss of European cooperation and the emergence of a nuclear-armed Iran. As my German interlocutor put it, ‘Trump must be told that he cannot have his cake and eat it.’