The republicans could have passed this when they had majorities in both houses + the president and didn't. They didn't do it then and they won't force it now. DCs gun ordinances make too good of a punching bag for interested parties on that side of the aisle to just legislate them away.
That was before McDonald where the SCOTUS declared 2A as a "Fundemental Right".
The irrony: to manage DC, the legislature doesn't need a presidential signature.