"The President, the Military and Minneapolis: What You Need to Know"
…."But there are two Insurrection Act provisions that can be invoked by the president
irrespective of a state's request or underlying desires.
"Ironically, presidents have actually relied upon these provisions to uphold civil rights and protect the rights of minorities in the Deep South during the 1950s and 1960s.
"The Insurrection Act authorizes the President to deploy the military (federal or state) whenever he believes it necessary “to suppress an insurrection, domestic violence, unlawful combination or conspiracy.” The full body of this provision states:
"Whenever the President considers that unlawful obstructions, combinations, or assemblages or rebellion against authority of United States makes it impracticable to enforce the law of the United States in any State or territory by judicial proceedings, the President may call into Federal service the militia of any State and use the Federal military to enforce the laws or suppress the rebellion.
"Third, the president can use the armed forces when there is an interference with federal or state law. The most generalized provision, its precise scope also remains largely untested. The president may use the military to suppress insurrection, domestic violence, unlawful combination or conspiracy if
"(a) it so hinders the execution of law of that State and of the United States and it deprives citizens of constitutional rights (e.g. due process); or (b) it opposes or obstructs the execution of laws or impedes the course of justice. In the event of the deprivation of rights, the State is deemed to have denied its citizens equal protection of laws.
"Finally, prior to invoking the Insurrection Act, the president, with the assistance of the attorney general,
'must first issue a proclamation to disperse.'
These final two provisions were invoked in the 1950s and 1960s, when presidents used them to enforce civil rights laws and end segregation in the South. Presidents Dwight Eisenhower and John Kennedy used these provisions in Arkansas, Alabama, and Mississippi to enforce civil rights laws. Kennedy invoked the interference with federal law provision to send federal military troops to Birmingham, Alabama during the civil rights protests.
In sum, invoking the Insurrection Act remains a rare occurrence in U.S. history, used in the most extraordinary circumstances, such as the complete disregard for enforcing federal civil rights laws or massive unrest in the nation’s second largest city. Despite the Insurrection Act’s invocation in Los Angeles, it has not been used in 28 years. And it was not invoked in Ferguson, Missouri. Nor was it invoked in Baltimore, Maryland during the riots that occurred in the aftermath of the death of Freddie Gray, who was killed by police officers in 2015. Nor was it invoked in the aftermath of Hurricane Katrina. Finally, it remains unclear whether the invocation of these two provisions are subject to judicial review. Courts have historically been reluctant to wade into these complex federalism and separation of powers waters and will certainly be wary of providing specific guidance."
https://www.justsecurity.org/70482/the-president-the-military-and-minneapolis-what-you-need-to-know/