Got a link to that? Trump didn't do that, it preceded him by many years. From the DCNG's own site:
Supervision and control of DCNG was delegated by the President of the United States to the Secretary of Defense pursuant to Executive Order 10030 in
Jan. 26, 1949, with authority given to the Secretary to designate officials of the National Military Establishment to administer affairs of the DCNG.
The DCNG is the only U.S. military force empowered to function in a state or, in this case, a district status. Those functions range from limited actions during non-emergency situations to full- scale law enforcement of martial law when local law enforcement officials can no longer maintain civil control.
The National Guard may be called into federal service in response to a call by the President or Congress.
For whatever reasons, neither the POTUS or Congressional leadership chose to use their power and waited for the Secty of Defense and the Secty of the Army to give the OK,
which was 4.5 hours after the violence had started.
The head of the DC NG, General Walker, almost chose to go in without permission and told some "go in now, resign tomorrow".