President Barack Obama and Afghan President Hamid Karzai sign a strategic partnership agreement at the presidential palace in Kabul, Afghanistan, Wednesday, May 2, 2012. (AP Photo/Charles Dharapak) President Barack Obama is greeted by Lt. Gen. Curtis "Mike" Scaparrotti, left, and U.S. Ambassador to Afghanistan Ryan Crocker, second left, as he steps off Air Force One at Bagram Air Field in Afghanistan, Tuesday, May 1, 2012. (AP Photo/Charles Dharapak) President Barack Obama is greeted by Lt. Gen. Curtis "Mike" Scaparrotti, and U.S. Ambassador to Afghanistan Ryan Crocker as he steps off Air Force One at Bagram Air Field in Afghanistan, Tuesday, May 1, 2012. (AP Photo/Charles Dharapak) President Barack Obama is greeted by Lt. Gen. Curtis "Mike" Scaparrotti, and U.S. Ambassador to Afghanistan Ryan Crocker as he steps off Air Force One at Bagram Air Field in Afghanistan, Tuesday, May 1, 2012. (AP Photo/Charles Dharapak) President Barack Obama and Afghan President Hamid Karzai arrive before signing a strategic partnership agreement, Tuesday, May 1, 2012, at the presidential palace in Kabul, Afghanistan. (AP Photo/Charles Dharapak) President Barack Obama and Afghan President Hamid Karzai arrive before signing a strategic partnership agreement, Tuesday, May 1, 2012, at the presidential palace in Kabul, Afghanistan. (AP Photo/Charles Dharapak) Security vehicles can be seen as President Barack Obama's motorcade drives to the presidential palace, in Kabul, Afghanistan, Tuesday, May 1, 2012, where he will meet with Afghan President Hamid Karzai and sign a strategic partnership agreement. (AP Photo/Charles Dharapak) President Barack Obama's motorcade drives to the presidential palace in Kabul, Afghanistan, Tuesday, May 1, 2012, where he will meet with Afghan President Hamid Karzai and sign a strategic partnership agreement. (AP Photo/Charles Dharapak) Arriving in darkness, members of the press and the President Barack Obama's entourage walk from Air Force One to waiting helicopters at Bagram Air Field in Afghanistan, Tuesday, May 1, 2012. (AP Photo/Charles Dharapak) White House Senior Adviser David Plouffe, center, talks with Senate Armed Services Committee Chairman Sen. Carl Levin, D-Mich., right, and committee member Sen. Jack Reed, D-R.I., as President Barack Obama and Afghan President Hamid Karzai met at the presidential palace in Kabul, Afghanistan, Tuesday, May 1, 2012. (AP Photo/Charles Dharapak) President Barack Obama and Afghan President Hamid Karzai sign a strategic partnership agreement at the presidential palace in Kabul, Afghanistan, Wednesday, May 2, 2012. (AP Photo/Charles Dharapak) President Barack Obama and Afghan President Hamid Karzai shake hands after making statements before signing a strategic partnership agreement at the presidential palace in Kabul, Afghanistan, Wednesday, May 2, 2012. (AP Photo/Charles Dharapak) President Barack Obama and Afghan President Hamid Karzai speak before signing a strategic partnership agreement at the presidential palace in Kabul, Afghanistan, Wednesday, May 2, 2012. (AP Photo/Charles Dharapak)