Should either Russia or the United States use tactical nuclear weapons, there will be both outrage and rationalization. The danger is this: If tactical nuclear weapons are used, it may not be possible to restore that stigma, let alone deterrence. If Trump uses tactical nuclear weapons against Pickaxe Mountain, every small state will demand the right to the same technology. What policymakers must then determine is how to re-establish the stigma surrounding nuclear weapons use. And that, more than any Pentagon planning for potential nuclear war, is what policymakers should now focus.