The first option, helping Ukraine win, is the most emotionally appealing and would certainly be the most morally justifiable and politically beneficial, but the risks and costs are high. Russia won’t accept defeat before trying every tactic, however brutal, and perhaps every weapon, however murderous. To force Russia to accept failure in Ukraine, the Biden administration would likely have to shift to a wartime mentality, perhaps including the kind of nuclear brinkmanship not seen since the Cuban missile crisis of 1962. With China and Iran both committed to weakening American power by any available means, a confrontation with the revisionist powers spearheaded by Russia may prove to be the most arduous challenge faced by an American administration since the height of the Cold War.

But the other two options are also bad. A Russian victory would inflict a massive blow to American prestige and the health of the North Atlantic Treaty Organization, especially if the West were seen as forcing Ukraine to surrender to Russian demands. Freezing the conflict is also perilous, as this would presumably leave Russia holding even more Ukrainian territory than it did following the 2014 invasions of Crimea and the Donbas. It would be hard to spin this as anything but a partial victory for Russia—and Mr. Putin would remain free to renew hostilities at a time of his choosing.