The United States has never renounced the right to use nuclear weapons first. The Obama administration narrowed the role of nuclear weapons by stating that the US would not use or threaten to use nuclear weapons against any country without nuclear weapons that was in compliance with its nuclear nonproliferation obligations.

But it stopped short of declaring that the sole purpose of US nuclear weapons was to deter the use of nuclear weapons. Instead, it cited “a narrow range of contingencies” in which US nuclear weapons might be used: to deter an attack on the US or its allies using conventional, chemical, or biological weapons by a state that possessed nuclear weapons or was not in compliance with its nonproliferation obligations. The Trump administration’s recent Nuclear Posture Review broadens the range of scenarios that might lead to the first use of US nuclear weapons. These, it says, “include, but are not limited to, attacks on the U.S., allied, or partner civilian population or infrastructure, and attacks on U.S. or allied nuclear forces, their command and control, or warning and attack assessment capabilities.”

“It defies human nature to build trust when weapons remain postured for mutual assured destruction. Washington and Moscow together must carefully dismount the “nuclear tiger” by reducing first-strike capabilities and fears, increasing warning and decision time for leaders and improving the survivability of their nuclear forces.”
Former Senate Armed Services Committee Chair, Sam Nunn

Substantially broadening the range of circumstances under which the United States would consider the first use of nuclear weapons is a step in the wrong direction. It makes a nuclear war more likely by reducing the threshold for nuclear use. Retaining the option to use nuclear weapons as part of a preemptive or preventive strike, or in response to conventional, chemical, biological, or other types of weapons creates a dangerous uncertainty. It makes it more likely that an adversary facing the threat of US nuclear weapons use may decide that it needs to be the first to take this step.. Given the overwhelming strength of its conventional military, the United States has nothing to gain from  escalating a conflict to the nuclear level. Indeed, the United States and the world have everything to lose.

The United States should instead declare that it will never be the first to use nuclear weapons, and would use them only in response to a previous nuclear attack. Such a “no first use” declaration would reduce the likelihood that tensions or conventional conflict with another nuclear-armed state would escalate to nuclear use.