President Donald Trump gave a speech on June 1, 2020 in which he promised to use military force against peaceful protesters. This speech took place just after military police attacked a crowd of peaceful demonstrators to clear a path to St. John's Episcopal Church so that he could walk over there with his bible. As disturbing as this unjustified use of force was, it pales in comparison to his speech.
In the speech he called himself American's "President of law and order," directed all governors to deploy the National Guard in force to put down all protests, and vowed to deploy the United States Army as well as other military forces to any state that fails to put down the protests. Trump has labeled the protests civil unrest instead of civil disobedience, he called out Antifa by name calling them a domestic terrorist group, and promised that everyone involved in recent protests will be punished to the full extent of the law.
President Trump has invoked the Insurrection Act of 1807 which allows the President to deploy active duty military personnel on American soil to quell rebellion. You can find the act at https://www.law.cornell.edu/uscode/text/10/subtitle-A/part-I/chapter-13 relevant portions read:
10 U.S. Code 252. Use of militia and armed forces to enforce Federal authority
Whenever the President considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings, he may call into Federal service such of the militia of any State, and use such of the armed forces, as he considers necessary to enforce those laws or to suppress the rebellion.
10 U.S. Code 253. Interference with State and Federal law
The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy, if it -
(1) so hinders the execution of the laws of that State, and of the United States within the State, that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law, and the constituted authorities of that State are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection; or
(2) opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.
In any situation covered by clause (1), the State shall be considered to have denied the equal protection of the laws secured by the Constitution.
10 U.S. Code 254. Proclamation to disperse
Whenever the President considers it necessary to use the militia or the armed forces under this chapter, he shall, by proclamation, immediately order the insurgents to disperse and retire peaceably to their abodes within a limited time.
10 U.S. Code 252. Use of militia and armed forces to enforce Federal authority
Whenever the President considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings, he may call into Federal service such of the militia of any State, and use such of the armed forces, as he considers necessary to enforce those laws or to suppress the rebellion.