I think Trump should direct the DOJ to look at law suit options to get a case up to the Supreme Court as soon as possible.
District of Columbia v. Heller, 554 U. S. 570 (2008)
It is settled that the Second Amendment protects an individual right to keep and bear arms that applies against both the Federal Government and the States.
McDonald v. City of Chicago
A case in which on June 28, 2010, the U.S. Supreme Court ruled (5–4) that the Second Amendment to the U.S. Constitution, which guarantees The right of the people to keep and bear Arms, applies to state and local governments as well as to the federal government.
United States v. Cruikshank (1876)
The Supreme Court ruled that, The right to bear arms is not granted by the Constitution; neither is it in any manner dependent upon that instrument for its existence.
The Second Amendment means no more than that it shall not be infringed by Congress, and has no other effect than to restrict the powers of the National Government.