U.S. Secretary of Defense Robert Gates (front L) and Afghanistan's President Hamid Karzai walk to an outdoor news conference through the grounds of the Presidential Palace in Kabul June 4, 2011. Gates arrived on his final trip to Afghanistan as Pentagon chief on Saturday, acknowledging Americans have grown tired of war but warning that success was imperative because failure would be the most costly result. REUTERS/Jason Reed (AFGHANISTAN - Tags: POLITICS MILITARY)