U.S. troops patrol in the Baraki Barak district of Logar province, Afghanistan. Sean Carberry/NPR hide caption

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U.S. soldiers carry a comrade injured by an improvised explosive device, or IED, in Logar province, south of Kabul, on Oct. 13. Roadside bombs are one of the biggest threats facing U.S. and Afghan troops, and insurgents keeping finding inventive ways to disguise them. Munir Uz Zaman/AFP/Getty Images hide caption

itoggle caption Munir Uz Zaman/AFP/Getty Images

Afghan soldiers stand at attention during a ceremony transferring authority from NATO-led troops to Afghan security forces in Afghanistan's Kunar province. The transfer of responsibility for security from NATO-led ISAF forces to Afghan troops is scheduled to be completed by the end of 2014. Rahmat Gul/AP hide caption

itoggle caption Rahmat Gul/AP

Nick Staback, who lost both of his legs to a bomb in Afghanistan, talks with his mother, Maria Staback, in Scranton, Pa. Maria Staback took a leave of absence from her job to move in with her son while he was recuperating at Walter Reed National Military Medical Center outside Washington, D.C. David Gilkey/NPR hide caption

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Sgt. Ben Roberts (center), recently returned from Afghanistan, speaks with Chick-fil-A manager Michael Sims at a military job fair in Columbia, S.C., in January. John Moore/Getty Images hide caption

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American director Sam French on the set of his short film, Buzkashi Boys, which was filmed in Afghanistan. David Gill/Courtesy of Afghan Film Project hide caption

itoggle caption David Gill/Courtesy of Afghan Film Project

Afghan children run to school on Sept. 24. Whoever takes over as the next U.S. president will have to determine how many troops will remain after the December 2014 deadline to help with long-term security. Jeff Pachoud/AFP/Getty Images hide caption

itoggle caption Jeff Pachoud/AFP/Getty Images

Blood stained the ground at the scene today in Khost, where a suicide bomber struck. Anwarullah /Reuters /Landov hide caption

itoggle caption Anwarullah /Reuters /Landov