Washington DC is affectionately called Chocolate City, not out of racism but out of a recognition of a black majority. If Trump can cause enough black people to demonstrate against the military presence in DC he may put his troops to use by having a mass shooting.
In his first term, he wanted to shoot demonstrators in the legs.

He has plans to federalize other cities with black mayors.
Trump does not have the legal authority to deploy National Guard troops in our cities beyond 30 days without congressional approval.
So far, that hasn't stopped his performance in LA with his toy soldiers.