President Obama, accompanied by Maj. Gen. Jeffrey S. Buchanan, left, commander of the U.S. Army Military District of Washington, lays a wreath at the Tomb of the Unknowns, with the aid of Sgt. 1st Class John C. Wirth, on Memorial Day, Monday, May 25, 2015, at Arlington National Cemetery in Arlington, Va. (AP Photo/Pablo Martinez Monsivais)