The NATO alliance has in recent years survived existential challenges - ranging from the war in Ukraine to multiple bouts of pressure and insults from US President Donald Trump, who has questioned its core mission and threatened to seize Greenland.
But it is the US-Israeli war with Iran, thousands of miles from Europe, that has nearly broken the 76-year-old bloc and threatens to leave it in its weakest state since its creation, say analysts and diplomats.
Trump, enraged that European countries have declined to send their navies to open up the Strait of Hormuz to global shipping following the start of the air war on Feb 28, has declared he is considering withdrawing from the alliance.
"Wouldn't you if you were me?" Trump asked Reuters in a Wednesday interview.
In a speech on Wednesday night, Trump criticized US allies but stopped short of condemning NATO, as many experts thought he might.
But combined with other barbs aimed at Europeans in recent weeks, Trump's comments have provoked unprecedented concern that the US will not come to the aid of European allies should they be attacked, whether or not Washington formally walks away.
The result, say analysts and diplomats, is that the alliance created in the Cold War that has long served as the basic fabric of European security is fraying and the mutual defense agreement at its core is no longer taken as a given.
"This is the worst place (NATO) has been since it was founded," said Max Bergmann, a former State Department official who now leads the Europe, Russia, and Eurasia Program at the Center for Strategic and International Studies in Washington.
"It's really hard to think of anything that even comes close."
That reality is sinking in for Europeans, who have counted on NATO as a bulwark against an increasingly assertive Russia.
As recently as February, NATO Secretary-General Mark Rutte had dismissed the idea of Europe defending itself without the US as a "silly thought." Now, many officials and diplomats consider it the default expectation.
"NATO remains necessary, but we must be capable of thinking of NATO without the Americans," said General Francois Lecointre, who served as France's armed forces chief from 2017 to 2021.
"Whether it should even continue to be called NATO - North Atlantic Treaty Organization - is a valid question."
White House spokeswoman Anna Kelly said: “President Trump has made his disappointment with NATO and other allies clear, and as the President emphasized, ‘the United States will remember.’”
A NATO representative did not immediately respond to a request for comment.
THIS TIME IT'S DIFFERENT
NATO has been challenged before, not least during Trump's first term from 2017 to 2021, when he also considered withdrawing from the alliance.
But while many European officials until recently believed that Trump could be kept on board with pomp and flattery, fewer now hold that belief, according to conversations with dozens of former and current US and European officials.
Trump and his officials have expressed frustration over what they see as NATO's unwillingness to help the United States in a time of need, including by not directly assisting with the Strait of Hormuz and by restricting US use of some airfields and airspace. US officials have declared NATO cannot be a "one-way street".
European officials counter that they have not received US requests for specific assets for a mission to open the strait and complain that Washington has been inconsistent about whether such a mission would operate during or after the war.
"It's a terrible situation for NATO to be in," said Jamie Shea, a former senior NATO official who is now a senior fellow at the Friends of Europe think tank.
"It is a blow to the allies who, since Trump returned to the White House, have worked hard to show that they are willing and able to take more responsibility (for their own defense)."
Trump's latest comments follow other signs of an increasingly unsteady alliance.
Those include his stepped-up threats in January to wrest Greenland away from Denmark and recent moves by the US that Europeans see as particularly accommodating toward Russia, which NATO defines as its principal security threat.
The administration has remained essentially mum amid reports that Moscow has provided targeting data for Iran to attack US assets in the Middle East and has lifted sanctions on Russian oil in a bid to ease global energy prices that have spiked during the war.
At a meeting of G7 foreign ministers near Paris last week, US Secretary of State Marco Rubio and Kaja Kallas, the foreign policy chief of the European Union, had a tense exchange, according to five people familiar with the matter, underlining the increasingly fraught transatlantic relationship.
Kallas asked when US patience with Russian President Vladimir Putin would run out over Ukraine peace negotiations, prompting Rubio to respond with irritation that the US was trying to end the war while also providing support to Ukraine, but the EU was welcome to mediate if it wanted to.
NO GOING BACK
Legally, Trump may lack the authority to withdraw from NATO. Under a law passed in 2023, a US president cannot exit the alliance without the consent of two-thirds of the US Senate, a nearly impossible threshold.
But analysts say that, as commander-in-chief, Trump can decide whether the US military will defend NATO members. Declining to do so could imperil the alliance without a formal withdrawal.
To be sure, not everyone sees the current crisis as existential. One French diplomat described the president's rhetoric as a passing temper tantrum.
Trump has changed his position on NATO before.
In 2024, he said on the campaign trail that he would encourage Putin to attack NATO members that do not pay their fair share on defense. By the last annual NATO summit, in June 2025, the alliance was in his good graces, with Trump delivering a speech effusively praising European leaders as people who "love their countries."
Next week, Rutte, the NATO secretary-general, who has a strong relationship with Trump, is set to visit Washington in an effort to change Trump's view once again.
Analysts say European nations have good reason to keep the US engaged in NATO despite doubts over whether Trump would come to their defense. Among other reasons, the US military provides a range of capabilities NATO can't easily replace, such as satellite intelligence.
Even if Trump and the Europeans find a way to stay together in NATO, diplomats, analysts and officials say, the transatlantic alliance that has been central to the global order since World War Two may never be the same.
"I do think we're turning the page of 80 years of working together," said Julianne Smith, the US ambassador to NATO under Democratic President Joe Biden.
"I don't think it means the end of the transatlantic relationship, but we're on the cusp of something that's going to have a different look and feel to it."
