JOINT BASE ANDREWS, Md. --   Col. Bill Knight, 11th Wing/Joint Base Andrews commander, and his wife Susan, wait to greet President Barack Obama and First Lady Michelle Obama Dec. 11, 2013. The President and first lady, along with former President George H.W. Bush and First Lady Laura Bush, were returning to the states after attending memorial services for former South African President, Dr. Nelson Mandela. (U.S. Air Force photo/Senior Airman Lindsey A. Porter)