A high-capacity magazine weapon was found Tuesday in a car belonging to a man visiting the Trump International Hotel.
Lee McCartney, 49, from Norristown, Pennsylvania, faces several charges including possessing an unregistered weapon.
McCartney tried to go through security for an event at the hotel and, when asked, told screeners he had a gun in his car, according to officials.
Police found a handgun and a high capacity magazine with 15 hallow point bullets in McCartney's Jeep. Police say he did not make any threats.
However, D.C. does not recognize weapon registrations from other states except under limited conditions.
D.C. Police took over the investigation from the Secret Service.