** FILE ** President Barack Obama steps off Marine One upon arrival at Andrews Air Force Base, Md., Wednesday, Sept. 5, 2012, before boarding Air Force One en route to Charlotte, N.C., for the Democratic National Convention. ( AP Photo/Jose Luis Magana)

Photo by: Jose Luis Magana

** FILE ** President Barack Obama steps off Marine One upon arrival at Andrews Air Force Base, Md., Wednesday, Sept. 5, 2012, before boarding Air Force One en route to Charlotte, N.C., for the Democratic National Convention. ( AP Photo/Jose Luis Magana)