The use of the military on public streets has happened before and the rules are a bit fuzzy. Federal troops were deployed during the 1992 Los Angeles riots that were sparked by the acquittal of police officers in the beating of Rodney King. President George H.W. Bush invoked the Insurrection Act to send in troops, including army and marine units, along with riot-trained federal law enforcement officers, to restore order. This decision was made after state and local efforts to quell the unrest, including the deployment of the National Guard, proved insufficient.

Going way back, troops fired on and killed protesting farmers on the Capitol steps.