North Korea has made significant strides in its attempt to acquire a strategic nuclear deterrent. In 2017, it tested intercontinental ballistic missiles (ICBMs) and completed a series of nuclear test explosions. These may provide North Korea with the technical foundation to deploy a nuclear-armed ICBM capable of striking the United States. The Ground-based Midcourse Defense (GMD) missile defense system is intended to deter North Korean nuclear coercion and, if deterrence fails, to defeat a limited North Korean attack. Despite two decades of dedicated and costly efforts, however, the GMD system remains unproven and unreliable. It has not demonstrated an ability to defeat the relatively simple and inexpensive countermeasures that North Korea can field. The GMD system has suffered persistent delays, substantial cost increases, and repeated program failures because of the politically motivated rush to deploy in the 1990s. But GMD and other U.S. missile defense efforts have provoked serious concerns in Russia and China, who fear it may threaten their nuclear deterrents. Diplomacy and deterrence may reassure Russia and China while constraining North Korea's nuclear program. An alternate airborne boost-phase intercept system may offer meaningful defense against North Korean missiles without threatening the Russian or Chinese deterrents.

As China invests in its nuclear forces and U.S.-China relations become increasingly strained, questions of U.S. nuclear doctrine require greater attention. The key strategic nuclear question facing the United States is whether to attempt to maintain and enhance its damage-limitation capability against China. The answer is less straightforward than it was during the Cold War, because China's nuclear force is orders of magnitude smaller than the Soviet force was. Part of the answer depends on the military-technical feasibility of the United States achieving a significant damage-limitation capability: What would be the outcome of military competition over the survivability of China's intercontinental ballistic missiles, submarine-launched ballistic missiles, and command and control, and over the effectiveness of U.S. ballistic missile defenses? The answer also depends on the benefits that a damage-limitation capability would provide; these could include contributions to homeland deterrence, extended deterrence, and reassurance of U.S. regional allies. The final piece of the analysis concerns the potential costs of a damage-limitation capability, which could include increased escalatory pressures during crises and growing political tension between the United States and China. A thorough analysis demonstrates that the United States should forgo such a capability because the prospects for preserving a significant damage-limitation capability are poor; the deterrent benefits would be small; and the escalatory and political costs would be relatively large.

Current U.S. nuclear strategy identifies new nuclear counterforce missions as a means of impeding the proliferation of weapons of mass destruction. The strategy appears to overvalue these counterforce missions. U.S. conventional weapons can destroy most targets that can be destroyed with nuclear weapons; only moderately deep and precisely located targets can be destroyed only by nuclear weapons. In addition, the benefits of nuclear counterforce-which could include deterrence, damage limitation, and the continued ability of the United States to pursue its foreign policy objectives-are relatively small, because the United States possesses large nuclear forces and highly effective conventional forces. Finally, nuclear counterforce would bring a variety of costs, including an increased probability of accidental war and unnecessary preemptive attacks in a severe crisis. Nevertheless, the case for nuclear counterforce is stronger than during the Cold War, when the enormous size and redundancy of U.S. and Soviet forces rendered counterforce useless. When facing a small nuclear force, the United States may decide to use counterforce to limit damage. Although complex trade-offs are involved, if there are critical targets that can be destroyed only with nuclear weapons, then under a narrow set of conditions the benefits of planning for damage limitation might exceed the dangers. The United States must not, however, rely on nuclear counterforce to support a more assertive foreign policy; doing so would unjustifiably increase the probability of nuclear war.