The DC National Guard began appearing in the nation’s capital on Tuesday after President Donald Trump announced a day earlier he is deploying guard troops and placing Washington, DC’s police department “under direct federal control,

At least six states have authorized National Guard troops to assist U.S. Immigration and Customs Enforcement (ICE) in administrative and logistical roles.

If President Trump deploys troops to other American cities, experts say it would be a clear departure from founding principles and invite a legal challenge.