Vladimir Putin’s recent announcement that he was not bluffing about using nuclear weapons against the West in his war on Ukraine is one of the strongest indications yet of the risks the liberal world now faces in opposing authoritarian aggression. In the face of Russian aggression, or in committing the United States to defending Taiwan, as President Joe Biden did yet again recently, Washington and its partners face the possibility of direct confrontation with the world’s most powerful, nuclear-armed militaries.