Trump has not invoked the Insurrection Act, which is the main legal tool a president can use to activate the military or National Guard when there is rebellion or unrest. But he hasn’t ruled it out, either. “Depends on whether or not there’s an insurrection,” Trump told reporters Sunday after a question about invoking the Insurrection Act.

Experts say it’s highly unusual for a president to call up the National Guard when the governor of a state objects. And Newsom is strongly in opposition.

In announcing the lawsuit, Attorney General Rob Bonta called the president's move to federalize the National Guard an "infringement" on state sovereignty.