Charter bus passengers look for their transportation home after the March on Washington of Aug. 28, 1963. AP hide caption

itoggle caption AP

Carnegie Mellon's autonomous car, developed with General Motors, is by all appearances a normal Cadillac SRX crossover — except for the big red button in the middle of the dashboard. In an emergency, the button allows the car to be switched immediately back to standard driving mode. GM-Carnegie Mellon Autonomous Driving Collaborative Research Lab hide caption

itoggle caption GM-Carnegie Mellon Autonomous Driving Collaborative Research Lab

U.S. Postal Service letter carrier Jamesa Euler delivers mail in the rain in Atlanta in February. David Goldman/AP hide caption

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President Obama has nominated John Koskinen to be commissioner of the Internal Revenue Service. Ron Edmonds/AP hide caption

itoggle caption Ron Edmonds/AP

Homeland Secretary Janet Napolitano, seen here testifying on Capitol Hill in February, announced her retirement earlier this month. As many as 15 other posts at DHS are now vacant or soon will be. Susan Walsh/AP hide caption

itoggle caption Susan Walsh/AP

A jet takes off from Reagan National Airport, near the Capitol. J. Scott Applewhite/AP hide caption

itoggle caption J. Scott Applewhite/AP

The Interstate 5 bridge over the Skagit River in Mount Vernon, Wash., collapsed last week. Elaine Thompson/AP hide caption

itoggle caption Elaine Thompson/AP