In his first term President Donald Trump episodically threatened to pull out of NATO, removing the United States as the linchpin of the most successful military alliance in modern times. In his second term, he is trying a different approach: hollowing it out from within.

Trump’s decision to reverse three years of unity in aiding Ukraine against Russia’s invasion and open negotiations with President Vladimir Putin has forced NATO leaders to confront a fundamental question: If Putin decided to pick off a member of the alliance, is there any reason to assume Trump would come to that country’s defense, the key to its strength?

“We have to assume not,” a senior member of the German government said at the Munich Security Conference, declining to speak on the record because of the huge sensitivity of his conclusion. In one short month as president, he and others contended, Trump has undercut the trust that sits at the center of the 75-year-old defense pact, that an attack on one member of the alliance would bring a response by all, led by the United States.

That fear has only accelerated in the past day, since Trump began echoing Putin’s talking points, falsely accusing Ukraine of provoking the invasion of its own territory and casting Russia as the aggrieved party rather than the aggressor. It is a rewriting of modern history that has left the NATO allies stunned and questioning the viability of an alliance with Washington at the center.

European officials knew when Trump was elected that the fundamental precepts of the post-World War II order would be threatened. They had been alarmed during the campaign when he said he would “encourage” the Russians “to do whatever the hell they want” to NATO members that did not contribute enough, in his view, to the alliance. They knew that even if the United States remained, on paper, the nuclear-armed behemoth at the center of NATO, Trump’s public musings could corrode the institution from within and undercut the goal of the alliance created in 1949 to confront the Soviet Union.

But the speed at which it has all unraveled has created a crisis of enormous proportions, at a time when European leadership is weak. Trump’s decision to impose tariffs, making no distinction between allies and adversaries, seemed harmful but manageable.

When his vice president, JD Vance, addressed the Munich Security Conference on Friday and seemed to embrace Alternative for Germany, which German intelligence has judged to be an extreme right-wing organization, the German defense minister, Boris Pistorius, told reporters that “this is not acceptable.”

But even as they left Munich, stunned, few in the European national security establishment seemed prepared for the possibility that Trump would not only threaten U.S. support for Ukraine, but also openly side with Putin and adapt his false line that Ukraine, not Russia, caused the conflict.

Fresh doubts

On Thursday, the United States was insisting that a standard-issue statement from the Group of 7 nations, drafted by Canada to mark the third anniversary of the invasion Monday, should be drastically shortened. Left on the cutting room floor, diplomats say, was much of the condemnation of Russia’s aggression and its violation of Ukraine’s sovereignty that were featured in similar statements issued during the first and second anniversaries. (Members of Trump’s inner circle, including Secretary of State Marco Rubio, were among those who condemned Russia’s actions until recent months.)

European officials suspect, based on what they heard last week from Defense Secretary Pete Hegseth, that tens of thousands of U.S. troops may be pulled out of Europe over the next few months or years. Hegseth was vague on the topic and offered no details. But here in Europe the only question is how many — and whether, when Trump is done, the U.S. military presence in Europe will have been whittled down to a symbolic ground force.

The most generous interpretation of Trump’s move is that he is forcing European nations to radically speed what they have long promised: to take a more central role in the Continent’s defense. But it is also true that Putin has been arguing for pullbacks of U.S. troops for years.

So far, few European leaders will publicly discuss the implications of a major drawdown. But Ukraine’s president, Volodymyr Zelenskyy, addressed it directly at Munich when he called for raising “an army of Europe,” independent of the United States.

Bernard-Henri Lévy, a prominent French commentator and philosopher, wrote this week: “Europe has no choice. The American president, the secretary of defense and the secretary of state have told us that we cannot depend indefinitely on the United States. We must unite or die. If we do not act, we will endure — in two, three or five years — a new Russian assault, but this time in a Baltic country, Poland or elsewhere.”

But the fact is, U.S. military officials say, Europe is far from ready.

Mistakes of the past

Before Trump’s remarkable reversal, U.S. military officials began executing a step-by-step, carefully coordinated handover of critical defense roles from American forces to European ones. But it is a yearslong process, American and European national security officials say, done carefully to make sure no gaps are left in defenses. A rapid U.S. withdrawal would leave huge vulnerabilities.

Fourteen years ago, as he was leaving the post of defense secretary, Robert Gates used his last speech in Europe to warn of what was coming.

“The blunt reality is that there will be dwindling appetite and patience in the U.S. Congress, and in the American body politic writ large, to expend increasingly precious funds on behalf of nations that are apparently unwilling to devote the necessary resources” to the military, and “to be serious and capable partners in their own defense.”

Three years later Putin seized Crimea from Ukraine, in what the Obama administration assumed would be a wake-up call for the NATO allies. It was not.

It took a year for Europe and the United States to agree on some fairly weak sanctions. The next year Angela Merkel, then Germany’s chancellor, struck a deal with Putin to build the Nord Stream 2 pipeline, making Europe more dependent on Russian gas.

Russia’s invasion of the rest of Ukraine three years ago finally prompted a rethinking. Germany opened up new lines of production for artillery, Finland and Sweden joined NATO out of fear and necessity, and more than 20 of the alliance’s members crossed the long-outdated threshold of spending 2% of their gross domestic product on defense.