In 1947 the U.S. Congress passed the National Security Act, which reorganized and renamed the Department of War, established in 1789, as the National Military Establishment. An amendment to the Act in 1949 changed the name of the National Military Establishment to the Department of Defense. Because the Constitution gives Congress the power to create executive departments and agencies, and because the Department of Defense was so named under Congressional legislation, President Donald Trump cannot legally reinstate the department’s official name under an executive order. In apparent recognition of that fact, the order eventually signed by Trump presents the new name as a “secondary title” of the department, though it also requires other federal departments and agencies to use the new name in official correspondence and nonstatutory documents.