On Wednesday, after America’s NATO allies refused his call to help unblock the Strait of Hormuz, a furious Donald Trump said he might withdraw the United States from the alliance. 

No other American president has even hinted at taking such a step: they all considered NATO vital to American national security as well as to global, particularly European, stability. Even if Trump does not act on his threat—his address to the nation left that question unresolved—Trump has broken new ground simply by making it.

Even the quarrel over the Strait of Hormuz likely won’t sink NATO. Still, Trump has put the alliance in a more precarious position than it has ever been in before. 

Trump’s long-game against NATO

Before turning to the alliance’s current crisis, it’s worth reviewing how things got to this point. 

By the time Trump was first elected in November 2016, the proposition that America’s NATO allies had to spend more on defense was axiomatic within the Washington establishment. Successive administrations insisted that allies get serious about “burden sharing.” 

At the alliance’s 2014 Wales summit, NATO agreed that each ally would allocate 2% of GDP to its defense budget by 2024.  By 2023, however, only a third of its 31 members—there are now 32—had met that goal. But ahead of the Vilnius summit that July, the entire alliance reaffirmed the 2% commitment.  

Burden-sharing had created discord within the alliance well before Trump’s first term began, but once his first presidency got underway, relationships started to deteriorate. What had been admonitions from Washington on defense expenditure turned into bluntly-delivered ultimatums. Trump publicly accused Europe of free-riding, and even called NATO “obsolete.” He took back that last criticism but piled on the pressure for additional allied defense spending. He questioned the alliance’s value to the United States and even sowed doubts about whether he’d protect Europe in the event of a Russian attack. At times, Trump did offer reassurances and affirmed NATO’s importance, but mostly, he was mercurial, dismissive, and confrontational. No other president has rattled America’s NATO allies to this extent—not even close. 

During Trump’s second term, the allies resorted to placation in response to his fulminations. Like........

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