US President Barack Obama's shadow is reflected on the Vietnam Veterans Memorial wall, etched with the names of US military members who died during the war, as he delivers remarks during an observance of the 50th anniversary of the Vietnam War, on the National Mall in Washington, May 28, 2012. [Photo/Agencies]

US President Barack Obama (R) stands with his wife Michelle Obama (2nd R), Defense Secretary Leon Panetta and Veterans Affairs Secretary Eric Shiseki (L) during an observance of the 50th anniversary of the Vietnam War, at the Vietnam Veterans Memorial wall in Washington, May 28, 2012. [Photo/Agencies]