U.S. President Barack Obama (2nd L) presents Defense Secretary Robert Gates (L) with the Presidential Medal of Freedom as Chairman of the Joint Chiefs of Staff U.S. Navy Admiral Michael Mullen (2nd R) looks on, during his farewell ceremony at the Pentagon in Arlington, Virginia, June 30, 2011. Gates is stepping down after four and a half years as the U.S. defense chief. REUTERS/Jonathan Ernst (UNITED STATES – Tags: POLITICS MILITARY)