For over a decade, U.S. President Donald Trump has accused Washington’s European allies of free-riding on American security guarantees. He has been criticizing NATO members that do not pay “their fair share” since launching his first presidential campaign in 2015. He threatened to pull out of the alliance after winning office, and then again when running for president in 2024. Just a few weeks ago, at a NATO meeting, U.S. Secretary of Defense Pete Hegseth announced a six-month review of the American military presence in Europe and declared that Washington’s payment of its annual NATO dues would be “contingent on other countries’ meeting their defense spending targets.” And at this month’s NATO summit in Turkey, the Trump administration’s threats to stop supporting Europe will surely hang over the proceedings.

The United States has suggested it might cut back its contributions to European security on many occasions since the end of the Cold War, but it has always come to the continent’s defense when required. When Europe proved unable to manage the war that broke out in Bosnia and Herzegovina in 1992, the United States intervened, paving the way for negotiations that ended the conflict. And even though Washington showed little appetite for coordinating a response to Russia’s annexation of Crimea in 2014, handing the diplomatic reins to France and Germany, the U.S. government stepped up after Russia’s full-scale invasion in 2022, offering strategic leadership and providing the bulk of NATO members’ military support to Ukraine. Throughout this time, the United States has pushed Europe to shoulder a greater share of NATO’s defense burden. But Europeans, confident that Washington would continue to support them when it counted, did not take this message as seriously as they should have.

The Trump administration has now challenged Europe’s sense of safety. It has downplayed U.S. interests in Ukraine, excluded European countries from talks to end the war there and from American deliberations to start a war with Iran, and eschewed formal processes to coordinate withdrawals of U.S. conventional forces from Europe. Unsure of the United States’ reliability and worried about facing Russian aggression alone, Europe has begun gathering the necessary resources to become a capable military power. The irony is that just as Europe becomes the kind of partner the United States should want on its side, Washington’s behavior has created a crisis of trust within the alliance. Now, if Washington cannot repair the damage it has done, it risks losing this ever more valuable ally altogether.

On paper, the transatlantic alliance is stronger and more balanced than ever. Almost all NATO members have met or exceeded the alliance’s defense spending target of two percent of GDP as of 2025, with spending increasing by 20 percent between 2024 and 2025. European allies and Canada now account for 40 percent of NATO’s total defense spending, up from 30 percent in 2020. If Europeans meet NATO’s 2035 targets, they would be spending more than $800 billion, a significant increase from Europe’s estimated total spending of $574 billion in 2025 and almost on par with the United States’ spending in 2025. In effect, the continent is beginning to do precisely what successive U.S. administrations have demanded for decades: assume greater responsibility for its own defense and thus enable Washington to focus resources elsewhere.

Yet a prolonged crisis of trust could erase any........

© Foreign Affairs