The U.S. President has sole authority to authorize the use of U.S. nuclear weapons. This authority is inherent in his
constitutional role as Commander in Chief. The President can seek advice from his senior military leaders; those military leaders are then required to transmit and implement the orders authorizing nuclear use if the President decides to employ nuclear weapons. As General John Hyten
stated in a congressional confirmation hearing, his job as the Commander of
U.S. Strategic Command (STRATCOM) would be to give advice, while the authority to order a launch lies with the President.
General Mark Milley, then the Chairman of the Joint Chiefs of Staff (CJCS), made a similar point in a
memorandum he provided to Congress in September 2021. He stated that he is a part of the "chain of communication," in his role as the President's primary military advisor, but he is not in the "chain of command" for authorizing a nuclear launch. He also stated that, if the President ordered a launch, the CJCS would participate in a "decision conference" to authenticate the presidential orders and to ensure that the President was "fully informed" about the implications of the launch.
The President, however, does not need the concurrence of either his military leaders or the U.S. Congress to order the launch of nuclear weapons. Neither the military nor Congress can overrule these orders. As former STRATCOM Commander General Robert Kehler has
written, members of the military are bound by the Uniform Code of Military Justice "to follow orders provided they are legal and have come from competent authority." But questions about the legality of the order—whether it is consistent with the requirements, under the laws of armed conflict (LOAC), for necessity, proportionality, and distinction—are more likely to lead to consultations and changes in the President's order than to a refusal by the military to execute the order.