He would have to get permission of the governor. I think there is a loop hole for DC because it has no governor.

"The Act (Posse Comitatus Act) does not prevent the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor."

  Wiki Page on the Posse Comitatus Act
  https://en.wikipedia.org/wiki/Posse_Comitatus_Act