Um, he has every right to do this. If anything the position of DC mayor/city council needs to be abolished and control returned back to where it belongs - Legislative/Executive branches. . .and before any dem/leftist bitch and moan about this, keep in mind DC didn't have a mayor until 1973. . .and look how it has turned out.
The Founders never intended the Capital to be ran like other local governments. They wanted the Capitol to be under federal jurisdiction. Perhaps it was meant to be litmus test to see if a President/Legislative branch can properly take of something like a city. . .if they can do that then they have the right to take of the country like they're supposed to. . .but if not, then out they go.