But if a cornered and delusional Mr. Putin were to instead use a nuclear weapon — whether via a tactical strike or by weaponizing one of Ukraine’s nuclear power plants — we would have several options.

There are some who would argue for a nuclear response. But there is a wide range of options, and they need not be mutually exclusive. For example, NATO could engage in Ukraine, potentially obliterating Russia’s struggling military. Further, we could confront China and every other nation with a choice much like that George W. Bush gave the world after Sept. 11: You are either with us, or you are with Russia — you cannot be with both.

Russia’s use of a nuclear weapon would unarguably be a redefining, reorienting geopolitical event. Any nation that chose to retain ties with Russia after such an outrage would itself also become a global pariah. Some or all of its economy would be severed from that of the United States and our allies. Today, the West represents over half of the global G.D.P. Separating any nation from our combined economies could devastate it. The impact on Western economies could be significant, but the impact on the economies of Russia and its fellow travelers would be much worse. It could ultimately be economic Armageddon, but that is far preferable to nuclear Armageddon.