Of all the warnings in President Trump's arsenal, quitting the NATO military alliance is among those he's wielded the most. Now he's doing it again. Asked by Britain's Telegraph newspaper if he is reconsidering US membership of NATO, he said: Oh yes… I would say [it's] beyond reconsideration – fuming again that his partners weren't joining America's military operations, alongside Israel, against Iran. I just think it should be automatic, he emphasised in his remarks to the paper.

Trump's invective underlines again his misunderstanding of how this 32-member alliance works. NATO's Article 5 commits it to collective defence. An attack against one member is deemed to be an attack against all, but invoking this principle requires a consensus. The 1949 treaty only referred to crises in Europe and North America, yet one ally after another has held back from joining a war they weren't consulted on, given they still don't understand its goals in the face of mixed messaging from the Trump administration.

Article 5 has only been triggered once, in the wake of the September 11th attacks on the US in 2001. Trump also referenced Ukraine in the Telegraph, saying: We've been there automatically, including Ukraine. After Russia's audacious full-scale invasion of Ukraine in February 2022, the then-US President Joe Biden did take a leading role in shaping the response of individual Western governments because he believed President Putin's actions threatened them all.

NATO, as an alliance, provided assistance but avoided the dangerous prospect of becoming directly involved as a party to this conflict. Even before Trump entered the White House in 2017, he repeatedly dismissed NATO as a paper tiger, described it as obsolete, and said that it was costing a fortune for the US.

This year, he's mocked the alliance, saying Russia would have occupied all of Ukraine if the US had not been NATO's enforcer. Trump almost walked out in early 2019, during his first term in office.

At the center of Trump's concerns was the 2014 agreement that countries should spend 2% of their GDP on defence; at the time, it was only described as a guideline. Military spending has ramped up significantly by almost all NATO members, partly in response to Trump's threats and partly because of Russia's growing menace.

The US's military budget now makes up some 62% percent of NATO's total defence spending, and the Pentagon has assets and intelligence capabilities others still can't match. This new crisis will again strengthen the resolve of European countries and Canada to bolster their own defences and depend on themselves for their security.

But there's still that cold hard fact that the might of the US military matters immensely. Trump's remarks have sparked discussions among his former allies, including Secretary of State Marco Rubio, who now advocates re-examining the US-NATO relationship.

NATO leaders, including the current Secretary General Mark Rutte, will likely continue their efforts to engage Trump and demonstrate the importance of the alliance for US interests. Rutte's attempts to keep the lines open with Trump highlight ongoing concerns about the future unity of NATO amidst shifting political landscapes and growing global threats.