FILE - This May 2, 2012 file photo shows President Barack Obama addressing troops at Bagram Air Field, Afghanistan. President Obama has made a surprise trip to Afghanistan for a Memorial Day weekend visit with U.S. troops serving in America’s longest war.(AP Photo/Charles Dharapak)
President Barack Obama gestures while speaking to troops at Bagram Air Field north of Kabul, Afghanistan, during an unannounced visit, on Sunday, May 25, 2014. (AP Photo/ Evan Vucci)
President Barack Obama gestures while speaking to troops at Bagram Air Field north of Kabul, Afghanistan, during an unannounced visit, on Sunday, May 25, 2014. (AP Photo/ Evan Vucci)
President Barack Obama shakes hands during a troop rally at Bagram Air Field, north of Kabul, Afghanistan, during an unannounced visit on Sunday, May 25, 2014. (AP Photo/ Evan Vucci)
President Barack Obama shakes hands during a troop rally at Bagram Air Field during an unannounced visit, on Sunday, May 25, 2014, north of Kabul, Afghanistan. (AP Photo/ Evan Vucci)
President Barack Obama shakes hands at a troop rally at Bagram Air Field, north of Kabul, Afghanistan, during an unannounced visit, on Sunday, May 25, 2014. (AP Photo/ Evan Vucci)