Also, the National Guard is STATE funded first and foremost. The feds may chip in, but it is a STATE organization. States control their NG units, decide promotions, etc., not the federal government. Yes, the President and Congress can nationalize them for service, but there is a procedure for that.
DC is not a state, nor even a territory is the common sense. It is a "federal district" according to the Constitution. That means the DC National Guard is funded by the substitute for a state, namely the federal government. The Commander-In-Chief is the President who acts as Governor of DC.
If nationalized, they cannot be used as law enforcement. But if left under state, or in this case federal district authority, they are very much law enforcement. So again, in DC, trump, and trump alone had the authority to call up the National Guard for law enforcement.