Remember the Eighth of May. History may recall it as the day the United States abandoned its belief in allies. Donald Trump’s exit from the Iran agreement puts Washington — rather than Tehran — in violation of an international deal. For the first time in decades, the US is acting without a European partner. The 2003 Iraq war was backed by Britain, Spain and others — along with halfhearted efforts to coax France and Germany. Mr Trump, by contrast, has isolated America from the rest of the west without serious effort at all. Who else could unify the post-Brexit UK with Europe?

The first casualty of Mr Trump’s move is any semblance of a global order. The US now finds itself in a lonely group with Israel and Saudi Arabia on one side of a toxic international breach. On the other are China, Russia, Europe and Iran. To that list we should almost certainly add Japan, India, Australia and Canada. It is hard to see how the gap will not widen. Mr Trump was deaf to the unanimous pleading of America’s closest allies. Two of their leaders, France’s Emmanuel Macron, and Germany’s Angela Merkel, even trekked to Washington in the last fortnight to press their case. They came away with nothing.

A third senior ally, Boris Johnson, Britain’s foreign secretary, pointed out that the world had “no Plan B” to the Iran nuclear deal. That was another way of saying that the alternative to “jaw jaw” is “war war”. Mr Trump has landed Europe with a dilemma it did its best to avoid. He is giving America’s leading Nato allies a choice between upholding a deal they brokered — and that Iran has honoured — or signing up to an “America first” war party over which they have no influence. The first will trigger US sanctions on European banks and energy companies that continue to do business with Iran. The second would mean forfeiting their best judgment and risking a Middle Eastern conflict that would hurt Europe far more than America. Falling in line with the US would also come at a steep political cost. Mr Macron’s domestic poll ratings fell after his “flattery offensive” on Mr Trump.