18 U.S. Code § 930 - Possession of firearms and dangerous weapons in Federal facilities(a)Except as provided in subsection (d), whoever knowingly possesses or causes to be present a firearm or other dangerous weapon in a Federal facility (other than a Federal court facility), or attempts to do so, shall be fined under this title or imprisoned not more than 1 year, or both.
[...]
(d)Subsection (a) shall not apply to—
(3)the lawful carrying of firearms or other dangerous weapons in a Federal facility incident to hunting or other lawful purposes.
Which, as I read it, makes carry of a handgun for self defense legal.
But the Postal Service reads it differently.
39 CFR § 232.1 - Conduct on postal property.(l) Weapons and explosives. Notwithstanding the provisions of any other law, rule or regulation, no person while on postal property may carry firearms, other dangerous or deadly weapons, or explosives, either openly or concealed, or store the same on postal property, except for official purposes.
It's not the statute that needs to be overturned, just the regulation.
But it seems this judge has tossed the statute. This matters, because the statute applies to all federal facilities, not just post offices.
But don't start carrying yet. This wasn't an injuction. The Post Office wasn't ordered to allow carry. This guy was charged with violating a number of laws, she dismissed the charge of carrying in a federal facility but allowed the other charges to stand. The ruling applies only to him, in this specific legal proceeding. It establishes no precedent.