We know what will not happen at NATO’s 75th anniversary summit in Washington this week: Ukraine becoming the alliance’s 33rd member. U.S. officials are talking instead about giving Ukraine “a bridge to NATO,” as National Security Council Senior Director for Europe Michael Carpenter put it recently. But when it comes to membership, many of the alliance’s leaders—including the United States and Germany—remain concerned that a formal move will be impossible as long as Kyiv is at war, given the centrality of the alliance’s Article 5 guarantee that an attack against one will be considered an attack against all.

Yet such concerns, while understandable, do not take sufficient account of either the current state of U.S. politics or the war itself. Ukraine’s “bridge to NATO” could easily become a bridge to nowhere if Donald Trump wins the November U.S. presidential election. Trump has threatened to withdraw from the alliance—or, as former NATO and Trump administration officials wrote together in Foreign Affairs recently, he could undermine the alliance by “withholding funding, recalling U.S. troops and commanders from Europe, and blocking important decisions in the North Atlantic Council.” He has also pledged to end the war in Ukraine in a single day.

Even without a Trump victory, it is unlikely that the flow of assistance from the U.S. and European governments will continue at anywhere near the levels of the past two and a half years. Chances of a major Russian advance or breakthrough will grow. Those could cause destabilizing refugee movements and panic among Russian border states (and beyond). Some countries might respond by doing what French President Emmanuel Macron proposed—sending their own forces to Ukraine, which could provoke retaliation against their NATO-protected home territories.

For the United States and its allies, securing Ukraine’s future shouldn’t be dismissed as an altruistic act that can be put off until later; it’s an act of self-defense that demands implementation now. Although bilateral accords are useful, they lack staying power at a time when elections scramble governments on both sides of the Atlantic. It’s hard to avoid seeing NATO membership as the most enduring solution to a conflict with potentially catastrophic consequences.

So how could Ukraine join the alliance in the near future, given that Russian troops are almost certain to occupy portions of its sovereign territory for years to come? History provides answers and precedents as to how to grant membership to a divided state—even one on the frontline. These historical models aren’t a perfect fit, their chances of working are far from certain, and the costs involved would be gut-wrenchingly high, because they include Ukraine ending major combat and provisionally tolerating division of its territory. Yet despite the costs, it’s time to consider these models seriously—because if any country deserves a hearing on some kind of creative way to become an ally as soon as possible, it’s Ukraine.

There’s room for creativity, because although NATO’s 1949 founding treaty does obligate allies to treat an attack on one as an attack on all, it doesn’t impose one-size-fits-all membership requirements, meaning that some countries have been able to negotiate bespoke terms. France, for example, remained an ally even after President Charles de Gaulle committed seemingly the ultimate dealbreaker in the mid-1960s—withdrawing from NATO’s integrated military command. Two other examples are even more relevant: Norway and West Germany, which both found ways to join the alliance despite, respectively, proximity to and conflict with Moscow.

Seventy-five years ago, Norway wanted what Ukraine wants today: to become an ally despite bordering Russia (then in the Soviet Union). Although Moscow wasn’t invading Norway at that time, or ever—in fact, the Red Army had even helped liberate some northern Norwegian territory from the Nazis—Norwegians had bitter memories of how their onetime neutrality had ended in brutal Nazi occupation. And they were horrified as........

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