By late August 2022, the West’s focus on Russia’s war in Ukraine was diminishing. The two sides were bogged down in an extended stalemate, freeing Western leaders from making difficult choices or thinking too hard about the future of the conflict. Events since early September—dramatic Ukrainian gains, followed by Russian mobilization, annexations, missile attacks on civilian areas, and nuclear threats—have shattered that illusion, pushing the war into a new and more dangerous phase.

Since the start of the war, the Biden administration has effectively maintained a balanced realpolitik approach: arming and funding Ukraine yet continuing to make clear that the United States will not engage directly in the conflict. But the administration has avoided talking about one crucial area of war strategy altogether: how it might end. Experts and policymakers who have suggested that the United States should also support diplomatic efforts aimed at a negotiated settlement have been treated as naïve or borderline treasonous. Driving the administration’s skittishness about endgames, then, are questions of morality: many argue that it is immoral to push Ukraine toward a settlement.

But nearly all wars end in negotiations. Moscow’s escalation this fall raises the twin specters of a broader war with NATO and of the use of nuclear weapons. The global economic costs of the conflict are already enormous and will almost certainly increase with the onset of winter. Even if a negotiated end to the war seems impossible today, the Biden administration should begin to raise—both publicly and to its partners—the difficult questions that such an approach would entail. It must think through the right timing to push for negotiations and at what point the costs of continuing to fight will outweigh the benefits. In seeking a sustainable settlement, the administration must also figure out how to capitalize on Ukraine’s successes without setting the stage for further conflict. To prepare for the best deal, American policymakers must maintain a common front between the West and Ukraine, take account of Ukrainian and Russian domestic politics, and embrace flexibility, particularly in working out which sanctions against Russia can be lifted without strengthening Putin’s regime. If the administration does not prepare soon, it may find its carefully calibrated response to the war being overtaken by a dangerous fantasy of absolute victory.