California Democratic Gov. Gavin Newsom is calling President Donald Trump's military intervention at protests over federal immigration policy in Los Angeles an assault on democracy and has sued to try to stop it.

The deployment of troops to Los Angeles raises questions about what Trump can and can't do with the military on U.S. soil, and whether he's crossing the line.

The standard to dispatch the military to a state is not simply in the eye of the beholder. There are limited legal circumstances in which a president is supposed to deploy the military domestically.