In this 2011 photo, U.S. soldiers board a U.S. military plane, as they leave Afghanistan, at the U.S. base in Bagram north of Kabul, Afghanistan. The Obama administration gave the first explicit signal Tuesday that it might leave no troops in Afghanistan after December 2014, an option that defies the Pentagon's view that thousands of troops may be needed to keep a lid on al-Qaida and to strengthen Afghan forces.

In this 2012 photo, President Barack Obama, right, shakes hands with with Afghan President Hamid Karzai, left, during their meeting at the NATO Summit in Chicago.