U.S. President Barack Obama, accompanied by Maj. Gen. Jeffrey S. Buchanan, commander of the U.S. Army Military District of Washington, and the with the aid of Sgt. 1st Class John C. Wirth, lays a wreath at the Tomb of the Unknowns, on Memorial Day, Monday, May 25, 2015, at Arlington National Cemetery in Arlington, Va. (DoD photo by Mass Communication Specialist 1st Class Daniel Hinton/released)