The U.S. Capitol and its office buildings were briefly locked down Tuesday after suspects nearby shot at District of Columbia police with a small machine gun. Police arrested three men after stopping their car about two blocks from the Capitol, Police Chief Cathy Lanier said. Police were alerted to a man with a gun near Fort McNair in southwest Washington, about a mile and a half south of the Capitol, shortly after 4 p.m., police spokesman Dustin Sternbeck said. Lanier said officers followed the car into a tunnel that goes under the National Mall near the Capitol. …