Putin, of course, is capable of making terrible choices, and he is desperate. Neither Ukraine nor the West can discount the possibility that he will order a nuclear attack. But the West can deter him by making it clear that, should Russia launch such a strike, it will directly, and conventionally, enter the conflict. Avoiding NATO involvement is one of the main reasons Putin continues to threaten a nuclear attack—Putin knows that if Russia cannot prevail against Ukraine, it has no chance against NATO—and he is therefore unlikely to do something that would bring the bloc in. That’s especially true given the speed with which NATO would win. Ukraine’s counteroffensive is moving comparatively slowly, giving Putin space to use his propaganda apparatus to manage public perception of the events. Once NATO joined, he would have no time to shield his reputation from the Russian military’s stunning collapse.
NATO has no shortage of ways to seriously threaten Russia without using nuclear weapons. It might not even need a land operation. The Western coalition could credibly tell the Kremlin that it would hit Russian capabilities with direct missile strikes and airstrikes, destroying its military facilities and disabling its Black Sea Fleet. It could threaten to cut all its communications with electronic warfare and arrange a cyber-blackout against the entire Russian military. The West could also threaten to impose sanctions that are totalizing and complete (no exceptions for energy buys), which would quickly bankrupt Russia. Especially if taken together, these measures would cause irreparable, critical damage to the Russian armed forces.
What the West should not and cannot do is be cowed by Russia’s nuclear blackmail. If the West stops aiding Ukraine because it fears the consequences, nuclear states will find it much easier to impose their will on nonnuclear ones in the future. If Russia orders a nuclear strike and gets away with it, nuclear states will have almost automatic permission to invade lesser powers. In either scenario, the result will be widespread proliferation. Even poorer countries will plow their resources into nuclear programs, and for an understandable reason: It will be the only sure way to guarantee their sovereignty.