Afghan National Security Adviser Mohammad Hanif Atmar (right) and U.S. Ambassador to Afghanistan James Cunningham exchange documents after signing the Bilateral Security Agreement, with Afghan President Ashraf Ghani (rear, left) and Chief Executive Abdullah Abdullah in the background. Jawad Jalali/EPA/Landov hide caption

itoggle caption Jawad Jalali/EPA/Landov

Afghan presidential candidates Abdullah Abdullah, left, and Ashraf Ghani Ahmadzai shake hands after signing a power-sharing pact in Kabul Sunday. The first vote in the election was held in April; a runoff followed in June. Wakil Kohsar/AFP/Getty Images hide caption

itoggle caption Wakil Kohsar/AFP/Getty Images

Abdullah Abullah (left) and Ashraf Ghani, shown here on August 8, have been contesting the results of Afghanistan's runoff presidential election for months. They are expected to sign a power-sharing deal on Sunday. Wakil Kohsar/AFP/Getty Images hide caption

itoggle caption Wakil Kohsar/AFP/Getty Images