That same risk applies in East Asia. The Trump administration appears to be holding up an $8 billion sale of F-16s to Taiwan, likely as a bargaining chip in trade negotiations with Beijing. But that can only further convince Chinese military planners that the U.S. has neither the political will nor adequate military means to help defend Taiwan in the event of an attack or invasion from the mainland.

The reunification of China by force would expose all U.S. security assurances as dubious, if not downright worthless. It would be an invitation to aggression by other revisionist powers in other theaters. It would also serve notice to countries like Japan, South Korea and Saudi Arabia to obtain nuclear arsenals of their own. Those who dislike nuclear weapons in the hands of the United States will dislike them even more in the hands of such states.

Hence the logic of U.S. nuclear deterrence, including the “extended deterrence” Republican and Democratic administrations furnished our allies for over 70 years. But that logic depends on maintaining a large, modern and calibrated arsenal that contains no gaps in a potential escalation cycle. Right now, the U.S. arsenal does have gaps, thanks to Russian treaty violations, is increasingly decrepit, thanks to delayed modernization, and may not be large enough in the face of not one, but two, major nuclear adversaries.