Commander-in-Chief Power

Article II makes the President commander in chief of the Army and Navy, and of state militias when called into federal service. The clause establishes civilian control of the military, a principle reinforced by the requirement that the Secretary of Defense be a civilian. Alexander Hamilton described the power in Federalist No. 69 as amounting to the supreme command and direction of the forces, distinct from the British king's power to declare war and raise armies, which the Constitution gives to Congress.

The President directs military operations, appoints and removes commanders, and alone holds authority to order the use of nuclear weapons. In the Prize Cases of 1863 the Supreme Court upheld Lincoln's blockade of Southern ports as a response to an attack the President had to meet. But the power has limits. In Youngstown in 1952 the Court held that it did not let Truman seize domestic steel mills, and in Hamdi v. Rumsfeld in 2004 and Hamdan v. Rumsfeld in 2006 it held that the President's wartime detention and military commissions remained subject to due process and congressional law.

Domestic use of the military is restricted by the Posse Comitatus Act of 1878, which bars the Army and Air Force from ordinary law enforcement, subject to exceptions such as the Insurrection Act. In 2025 the President federalized National Guard units and deployed troops to Los Angeles and other cities over the objections of governors, prompting lawsuits over the scope of his authority. The tension between the commander-in-chief power and Congress's war powers runs through every modern military operation.