President Trump has cited Title 10, U.S. Code, Section 12406 as the authority to deploy the National Guard to protect federal personnel and property.
§12406. National Guard in Federal service: call
Whenever-
(1) the United States, or any of the Commonwealths or possessions, is invaded or is in danger of invasion by a foreign nation;
(2) there is a rebellion or danger of a rebellion against the authority of the Government of the United States; or
(3) the President is unable with the regular forces to execute the laws of the United States;
The President may call into Federal service members and units of the National Guard of any State in such numbers as he considers necessary to repel the invasion, suppress the rebellion, or execute those laws. Orders for these purposes shall be issued through the governors of the States or, in the case of the District of Columbia, through the commanding general of the National Guard of the District of Columbia.
Section 12406 of Title 10 permits the President to call the National Guard into federal service under specific circumstances, including invasion, rebellion, or when unable to execute laws with regular forces.
Section 12406 is distinct from the Insurrection Act (10 U.S.C. § 251-255). The Insurrection Act specifically allows the president to use the military for civilian law enforcement during an insurrection, while Section 12406, when used alone, does not override the Posse Comitatus Act and restricts federalized troops to a supportive role, such as protecting property. The decision to use Section 12406 instead of the Insurrection Act may be due to its potentially lower political sensitivity, but it has resulted in legal ambiguity and debate over presidential authority.