Governors can request the federal government send active duty troops to help in cases of civil unrest like the widespread protests plaguing U.S. cities. But, so far, no state governors have requested active duty troops to assist and instead have relied on local law enforcement and National Guard soldiers and airmen on state active duty.
Governors often prefer the National Guard forces in these cases because they can legally perform law enforcement duties in the U.S., whereas troops on active duty cannot or they violate the Posse Comitatus Act.
But, the president could invoke the Insurrection Act to deploy active-duty troops without a request from a state. Those troops would be allowed to conduct law enforcement missions. To invoke the act, Trump would first have to issue a proclamation to “immediately order the insurgents to disperse and retire peaceably to their abodes within a limited time,” according to the law.