ARLINGTON, VA - NOVEMBER 11: U.S. President Barack Obama participates in a full honor wreath-laying ceremony at the Tomb of the Unknown Soldier at Arlington National Cemetery to commemorate Veterans Day November 11, 2015 in Arlington, Virginia. The tomb contains the remains of an unidentified soldier from World War I and crypts of unknowns from World War II, Korea and Vietnam are set next to the tomb. In 1998 DNA testing was able to identify the remains in the Vietnam soldier's crypt, which now remains empty. (Photo by Chip Somodevilla/Getty Images)
