Even worse, it's a federal district per the constitution and per the constitution the Congress writes laws for execution. Unfortunately, under our unitary executive arrangement, Trump has the executive power to ensure that the laws are being properly executed, whatever the arrangement for providing subordinate officers [mayor and DC legislature].
The question as I see it is, what is the DC government? Is it an agency? Then Trump has vast powers to fire the employees. Is it an alter ego of the U.S. Congress? Then, Trump’s powers may not be so sweeping.