For decades, collective European self-defense was merely an aspiration. Today, the time to realize this goal is finally at hand. Momentum in Europe is building: years of marginal steps to bolster European defenses gave way to meaningful action after Russia invaded Ukraine in 2022, and these efforts have accelerated in the six months since U.S. President Donald Trump came into office. European leaders promised a sharp increase in defense and defense-related spending at the NATO summit in June, raising members’ overall budget commitments from two percent to five percent of GDP. To make good on those crucial new pledges, Europe is introducing new financial mechanisms and breaking down barriers to cooperation in its defense industry.

The danger now is that Europe will lose its momentum—and that the United States, by delaying an expected drawdown of forces from the continent, will let it. Both sides have good reason to see Europe’s defense buildup succeed. The United States would be able to free up forces now stationed in Europe for other missions, or simply make cuts and pocket the savings. A more capable Europe would become the kind of partner that Washington wants and needs, and it would gain the freedom to set its own strategy as a global power.

To ensure that this necessary rebalancing proceeds, the Trump administration must withdraw substantial numbers of U.S. forces from Europe, starting now, and truly shift the burden of the region’s conventional defense onto the continent. Hesitating would undermine Europe’s progress and risk locking in a suboptimal security structure for years to come. To encourage Europe to follow through on its own promises, Washington must lay out a realistic, targeted, and phased plan that cuts U.S. troop levels in Europe roughly in half over the next four years while keeping in place forces vital to U.S. security interests or forces that Europe cannot reasonably replace in that time. If a drawdown is executed well, there is little reason to fear that it would end the transatlantic partnership or leave either side less safe.

The best window for Europe to take on a greater share of the burden for its defense is now—not in five or ten years when political will may have faded or an emergency elsewhere forces a sudden U.S. withdrawal. The reasons for making the change are not going away. Competition with China and the emergence of other global powers have altered the United States’ strategic reality. Washington can no longer maintain the global military primacy it enjoyed after the end of the Cold War. To avoid overstretching, the United States must allocate its assets prudently—which means withdrawing from or downsizing in some parts of the world. Not to do so would drain the country’s resources, worsening a domestic fiscal crisis and killing any hope of retaining the global military lead that the United States still enjoys. Every U.S. administration since President Barack Obama’s has recognized this imperative—in theory, if rarely in practice—and future administrations are very unlikely to think differently. The reality is that U.S. troop deployments in Europe are larger than necessary to defend core U.S. interests on the continent, so they will remain near the top of the list of cuts. This is not because Europe is unimportant to the United States but because many U.S. forces in Europe are unneeded given the current threat level and becoming redundant as Europe’s military might grows.

Russia, of course, is a serious threat to Europe and the United States. President Vladimir Putin despises both. He has sophisticated nuclear weapons, well-developed hybrid warfare and intelligence capabilities, and a large conventional force hardened by years of war against Ukraine. But not all of these capabilities directly threaten the United States. Russia’s long-range nuclear weapons and advanced cyber-capabilities put the United States at risk, as do Russian covert agents who spy, disrupt civil society, and have assassinated private citizens. Russian tanks and artillery, however, do not. Concentrating U.S. resources on nuclear, cyber, and gray-zone defense while leaving land defense largely to European allies will be a more sustainable division of responsibilities as Washington pares down its commitments.

The war in Ukraine is often cited as a reason to keep U.S. forces at........

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