Just eliminate 18USC 922 (o) and Chapter 4 of the 1968 GCA and watch liberal heads EXPLODE (as I go to the FN factory and order an FN M240 and M203).
There are several positive things President Trump can do without legislative action:
How President Trump can Defang Federal Gun Free Zones
http://gunwatch.blogspot.com/2016/11/how-president-trump-can-defang-federal.html