Plainclothes agents saw April Lenhart with the handgun holstered on the north side of the White House on Pennsylvania Avenue about 8:30 p.m., sources told ABC News. Uniformed agents who were alerted then arrested her.
Lenhart, 23, of Michigan, was with a man who wasn't arrested, according to sources. Secret Service agents hoped to get a search warrant to look through her car, which was nearby.
The incident came a day after R.J. Kapheim was arrested one block from the White House after a search of his car uncovered a rifle and ammunition.