Excerpt
President Trump Has The Power To Call Out The Troops
However, the president does have the authority to take command away from the governors and put the Guard into federal service under "Title 10,” the section of the U.S. code that covers the armed forces. The president could try to do this by using one of the federal mobilization authorities, but this requires a declaration of emergency, such as was made after the attacks of 9/11. The president could try to declare an emergency for domestic disturbances, but the statutory language clearly envisions an overseas emergency, and governors would immediately challenge this in court.
That brings us to the Insurrection Act. This old statue allows the president to take control of the National Guard in certain circumstances: “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.”
https://www.forbes.com/sites/markcancian/2020/06/02/the-president-has-the-power-call-out-the-troopsbut-shouldnt/?sh=5ea004ddf179