The Insurrection Act of 1807 is a United States federal law[1] that empowers the president of the United States to deploy U.S. military and federalized National Guard troops within the United States in particular circumstances, such as to suppress civil disorder, insurrection, or rebellion.
The act provides a "statutory exception" to the Posse Comitatus Act of 1878, which limits the use of military personnel under federal command for law enforcement purposes within the United States.[2][3]
Before invoking the powers under the Act, 10U.S.C. § 254 requires the President to first publish a proclamation ordering the insurgents to disperse.
Trump satisfied the requirement to disperse peacefully in his Twatter message that afternoon on J6. The same Tweet that Twitter removed from their platform almost immediately.
https://en.wikipedia.org/wiki/Insurrection_Act_of_1807