In July 2018, NATO’s gleaming new Brussels headquarters was poised to host its first leaders’ summit. Dignitaries from around the world gathered in the arched buildings designed to look like interlocking fingers. But the Europeans throwing the party were anxious. The nominal guest of honor, President Trump, had spent months questioning the need for U.S. membership in an organization that had emerged from the ashes of World War II as a bulwark against Moscow’s aggression. He soon ruined the festivities.During a closed-door meeting with other leaders, the president went on a tirade, berating the other nations for failing to spend the targeted 2 percent of their GDP on defense, urging better relations with Russia, and threatening to withdraw the United States from NATO if he didn’t get what he wanted. Trump eventually relented. But the very next week, he met Vladimir Putin at a summit in Helsinki and repeatedly sided with the Russian leader, who has made it his mission to undermine the alliance. Nearly eight years later, Putin may get his wish.Trump is now demanding that NATO help the United States reopen the Strait of Hormuz, a vital passage through which 20 percent of the world’s oil travels, which Iran has effectively closed in response to the United States’ and Israel’s attacks. NATO has refused. And though Russia is playing only a tangential role in the crisis there, Moscow could emerge as one of the victors of war. The standoff over the strait has created an unexpected new strain on the relationship between Trump and NATO, one that may not fully shatter the alliance but could fundamentally weaken it.“I think he made NATO defunct in practice already with Iran,” one senior European Union diplomat told us on the condition of anonymity to be candid about geopolitically sensitive subjects. And that diplomat made a grim prediction that Trump’s likely retaliation would be to reduce its troop numbers on the continent. “If we were not expecting his pullout of troops, we should be.”Trump had hoped that the attack on Iran would follow the blueprint established by the raid to seize Nicolás Maduro from Venezuela, his advisers have told us: a quick strike that removes the existing leadership, allowing for the installation of a more compliant figure atop the government. Although Ayatollah Ali Khamenei is dead, and thousands of Iranian military targets have been battered, the hard-line regime leaders in Tehran have remained in power, firing missiles at their Gulf neighbors and blocking access to the Strait of Hormuz—just as Pentagon officials and military think tanks have predicted for decades. General Dan Caine, the chairman of the Joint Chiefs of Staff, cautioned Trump in the run-up to the invasion, but the president dismissed the warning, believing that Iran would capitulate instead.He was wrong. Iran shuttered the strait. Oil prices have jumped more than 40 percent in the past month, and gas costs have soared at the pump for Americans. Any U.S. effort to reopen the waterway would carry danger. Though the Iranian navy has been crushed, it could still fill the strait’s waters with mines. Damaging an oil tanker or U.S. warship would take only a single drone—or a speedboat packed with explosives, or a rocket launched from ship or shore. If U.S. special forces were deployed on the ground to try to secure the strait, casualties would surely follow. So Trump instead asked other nations for help in keeping the waterway open, particularly European allies.[Read: How much pain is Trump really willing to endure?]Many European governments do not want to be pulled into military action, and they were frustrated that they had not been consulted by the Trump administration before the war. Plus, many feel lingering anger about Trump’s attempts to strong-arm Denmark into giving up control of Greenland earlier this year. That, in particular, was an inflection point for the alliance, a number of officials believe. Repeated offers from Europe—promising the U.S. access to bases, minerals, and more—went unheeded, and when Trump went to the World Economic Forum in January, some openly wondered whether the U.S. military would invade Greenland. Trump eventually backed down (for now). But the damage was done.In recent days, a few nations have offered help: France deployed warships to the region while Britain, after initially refusing, has allowed the U.S to use its military bases. NATO Secretary General Mark Rutte, who is proudly chummy with Trump, has pledged that members of the alliance would lend some form of assistance. But no one has signed up for the dangerous duty of escorting tankers through the strait. Even though Trump had not committed the U.S. Navy to doing that either, he raged against Europe’s reluctance, taking to social media last Friday to deem the other NATO members “COWARDS” and assert that “without the U.S.A., NATO IS A PAPER TIGER!” He suggested in an interview that NATO would have a “very bad” future if it did not change course. And then, this morning, Trump returned to social media to unleash an all-caps screed blasting NATO for doing “ABSOLUTELY NOTHING” to help and said that the United States will “NEVER FORGET” members’ obstinance.White House officials and those close to Trump told us that there are not active discussions to pull the U.S. out of NATO, but they emphasized that the cool response to his requests incensed the president, who would likely need little prompting to try to withdraw. To be clear, that would be difficult: The United States is a member via treaty, an area where the Senate has historically had a say. But a series of court decisions in the past 50 years has given the executive branch more leeway to withdraw from treaties. NATO’s own charter allows a nation to pull out after giving one year’s notice. The National Defense Authorization Act of 2024, signed into law by President Biden, prohibits a president from pulling the United States out of NATO without either a two-thirds Senate supermajority or an act of Congress. Trump might argue that treaty termination is an exclusive executive power, but the move would trigger a massive court battle—and likely a constitutional crisis.Still, Trump insisted to reporters last week that pulling out of the alliance is “certainly something that we should think about.” He added: “I don’t need Congress for that decision.” Even if he doesn’t try to withdraw, he has other options. He could slash U.S. funding for NATO. He could refuse to honor the Article 5 mutual-defense pact, essentially crippling the alliance. Or he could move U.S. troops out of Europe, redeploying them to Asia or the Middle East or bringing them back home, leaving the continent with diminished defenses against a Russian menace.Indeed, Trump has long threatened such a move. In July 2020, near the end of his first term, the Pentagon announced plans to reduce troop levels in Germany by a third. “Germany is not paying their bills,” Trump said at the time, referring to a commitment among NATO allies to spend at least 2 percent of their gross domestic product on defense. The following year, the House refused to fund the withdrawal, effectively blocking it. But Trump continued to pressure NATO to stop “freeloading” and take more responsibility for Europe’s security.[Read: Europe’s far right is turning on Trump]The allies have tried to placate him. A few months into Trump’s second term, they agreed at a summit in the Hague to raise their defense spending to 5 percent of GDP. The pledge did not seem to change Trump’s plans. In October, the U.S. Army said that about 3,000 troops from the 101st Airborne Division would end their deployment to Romania and go home “without replacement.” The Army’s Europe and Africa command, which is based in Germany, tried to reassure allies that this was not part of an American withdrawal from Europe. But many officials and military analysts saw it as a sign of the great unraveling they feared. “From Moscow’s perspective, the move will be applauded and seen as a weakening of US resolve,” Alex Șerban of the Atlantic Council think tank wrote at the time.Congress could resist any broader reduction of U.S. forces in Europe, which number roughly 85,000. Under the National Defense Authorization Act that Trump signed in December, the U.S. presence on the continent must remain at a minimum of 76,000 troops. But the start of the war in Iran has many European leaders worrying about a deeper break within NATO. Even Finnish President Alexander Stubb, who has cultivated a friendship with Trump over their shared love of golf, admitted that a “split” had formed in the Western alliance. “It’s a reality that I have to live with,” Stubb told The Telegraph. “And I obviously try to salvage what I can.”White House Press Secretary Karoline Leavitt told us in a statement that “President Trump has been very vocal and honest about his displeasure with NATO.”The Russians have tried to further deepen the rift. Already, they have supplied Iran with intelligence for targeting American assets in the region and have received no punishment from Washington. (Trump, in fact, continues to suggest that Ukrainian President Volodymyr Zelensky is more of an impediment to peace in Europe than Putin.) On March 11, the Kremlin envoy Kirill Dmitriev met in Florida with Trump’s old friend Steve Witkoff and his son-in-law Jared Kushner, who have become the White House’s lead negotiators for the conflict. By that point, the Iranians had blocked the Strait of Hormuz for nearly two weeks. Dmitriev offered a solution in a social-media post after the meeting: “Today, many countries, primarily the United States, are beginning to better understand the key, systemic role of Russian oil and gas in ensuring the stability of the global economy, as well as the ineffectiveness and destructive nature of sanctions against Russia.”The following day, the United States agreed to ease some of those sanctions for 30 days, lifting restrictions on the sale of Russian oil that had been loaded on tankers. New money would flow into Russia’s war machine as it continued to wage its war against Ukraine. Pundits on Russian state TV celebrated the move as a sign of Trump’s weakened position. “The U.S. has made a concession,” said Kirill Koktysh, a professor at Moscow’s main diplomatic academy. Moscow would be wise to take advantage of Trump’s party still being in power until the midterms, he said. “We have to get these concessions now, and not take any harsh or unequivocal conditions on ourselves.”It was a win for Putin. He may get another, larger one soon.