THE SUEZ crisis, the Vietnam war, the invasion of Iraq: non-European wars have a way of tearing at the fabric of NATO. Now America’s air campaign (alongside Israel) against Iran may rip the alliance apart. Donald Trump has grown increasingly hostile towards European allies, furious at their refusal to help America re-open the Strait of Hormuz. Worse, several European countries have made American operations in the Middle East more difficult.

“COWARDS, and we will REMEMBER!” blasted Mr Trump in one social-media post on March 20th. In recent interviews he said he was “absolutely” considering leaving the alliance, although he did not repeat the threat in a televised address about the Iran war on April 1st. The president’s imprecations have been echoed by Marco Rubio, his secretary of state, once a staunch defender of the transatlantic alliance. Calling NATO “a one-way street”, Mr Rubio declared: “There is no doubt, unfortunately, after this conflict is concluded we are going to have to re-examine that relationship.”

Mr Rubio’s shift has helped create a funereal mood in European capitals. As a senator, he co-sponsored a bipartisan law in 2023 to prevent the unilateral withdrawal that Mr Trump is now contemplating. “The President shall not suspend, terminate, denounce, or withdraw the United States from the North Atlantic Treaty […] except by and with the advice and consent of the Senate” by a two-thirds majority, declares the act. Now as one of the most important figures in the Trump administration, Mr Rubio appears to be recanting. He has often acted as the last grown-up in Mr Trump’s court, stepping in to steady transatlantic relations and prevent the full abandonment of Ukraine. The last constraint may now be gone.

“This is the worst moment that NATO has faced,” says Ivo Daalder, a former American ambassador to NATO. “Rather than trying to convince Donald Trump not to leave, allies have to focus…on strengthening their military capacity.” He said European refusal to facilitate the war had undermined pro-NATO Americans, who argue that Europe offers America a launch-pad to project power globally.

Spain’s Socialist prime minister, Pedro Sánchez, has been the most confrontational, barely meeting the old 2% of GDP target for defence spending, but rejecting the new one for 3.5% (plus 1.5% on defence-related infrastructure). Spain has closed its bases and airspace to American forces attacking Iran. France has been more measured. Its fighter jets have helped the United Arab Emirates shoot down drones, and it has sent an aircraft carrier to help defend Cyprus. Mr Trump has nevertheless lashed out at France’s “very unhelpful” refusal to let some American military aircraft fly over its territory.

Britain, having initially refused to let American forces use its bases, now permits it, but only to protect neighbouring countries from Iran’s retaliation. “This is not our war,” Sir Keir Starmer, the British prime minister, has repeatedly insisted. Mr Trump has retorted that Sir Keir is “no Winston Churchill”. Italy, another defence-spending laggard, reportedly stopped some American planes from using a base in Sicily. For Kurt Volker, another former American ambassador to NATO, European actions have been “foolish”, though understandable: “They are responding emotionally against Donald Trump, not rationally, in accordance with their interest.”

Mr Trump has toyed since his first term with the idea of withdrawing from NATO. Last year, however, he cast himself as the alliance’s saviour by convincing allies to spend at least 5% of GDP on defence and related infrastructure. Relations later soured again as Mr Trump wooed Russia. He outraged allies by reviving his campaign to seize Greenland, a self-governing territory of Denmark. The war in Iran is bringing resentment to a boil. American officials have suggested they may withhold weapons intended for Ukraine, partly out of frustration at the lack of progress in peace talks with Russia, and partly because America’s own stocks are running low.

Mr Volker still hopes Congress will stop Mr Trump from abandoning NATO. “It’s a red line for many Republicans—perhaps the only one,” he argues. But the 2023 law constraining Mr Trump from leaving NATO may be ignored or deemed unconstitutional. In any case, Mr Trump need not formally leave the alliance to cripple it: he could withdraw American forces from Europe, or recall its military commander, an American general. “I have spent the past five years telling people not to worry about Trump and NATO,” says one European diplomat in Washington, DC. “Now I am genuinely quite worried about Trump and NATO.”

Mark Rutte, the NATO secretary-general, who has raised eyebrows by on one occasion calling Mr Trump “daddy” and by endorsing his assault on Iran, is due to visit Washington on April 8th to try to soothe relations. Britain convened a video conference of about 40 countries on April 2nd—without America—to discuss ways of increasing political and economic pressure on Iran to re-open the Strait of Hormuz.

The international waterway carries about a quarter of global seaborne oil, not to mention similar shares of liquified natural gas and fertiliser. Since the start of the campaign on February 28th Iran has prevented all but a handful of ships—usually ones carrying its oil or from countries deemed friendly, such as India—from transiting daily in and out of the Persian Gulf. A French-owned container ship made the passage on March 28th. Iran is now talking about imposing a toll on ships seeking to use the strait.

“Iran is trying to hold the global economy hostage,” said Yvette Cooper, Britain’s foreign secretary, in a statement. Participants in the British teleconference, she added, called for “the immediate and unconditional reopening of the strait”. Those at a similar gathering on March 19th had declared themselves willing to contribute to “appropriate efforts to ensure safe passage through the strait”. Military chiefs are expected to discuss options for escorting ships at a meeting next week.

In his address on April 1st Mr Trump suggested he could end the war within weeks even if the strait remained closed. Iran had been “completely decimated”, he said. Countries that depended on the strait “must grab it and cherish it”, he added: “the hard part is done, so it should be easy.” Yet no American warship has yet run the gauntlet.

European countries say no escort mission is feasible until fighting has died down, and diplomats say there are disagreements over the terms of any such mission. Re-opening the strait by force would be “unrealistic”, insisted Emmanuel Macron, the French president, during a visit to South Korea. “First, there must be a ceasefire and a resumption of negotiations.” In that framework, he said, “reassurance missions may be possible.” Diplomats say France wants to lead the mission, exclude America and bring in India and perhaps China. Britain thinks Iran is unlikely to give up threatening ships; to protect allied forces, it thinks America should spearhead the mission. Mr Trump, for his part, says Europeans should “take the lead”, though America “will be helpful”.

One gloomy Finnish official thinks all this will make little difference. The situation may have gone “beyond the point” where European action could soften Mr Trump’s contempt for NATO. The alliance faces grim times ahead of its annual summit in Ankara in July. Its best option, he says, would be to redouble efforts to build the European pillar of NATO. Perhaps that would convince Mr Trump that allies are willing to take up more of the burden. More probably, it would at least start to prepare them for the daunting task of taking over NATO if Mr Trump abandons it.