Department of Homeland Security Secretary Kirstjen Nielsen and U.S. Air Force General Terrence J. O'Shaughnessy, commander of the North American Aerospace Defense Command and U.S. Northern Command, pose for a group photo with NORAD and USNORTHCOM senior leaders during the Secretary's visit to Peterson Air Force Base, Colorado, Sept. 6, 2018. O'Shaughnessy and Nielsen discussed agency's and the commands' complementary missions to protect and defend the United States against all threats. (U.S. Air Force photo by Tech. Sgt. Joe Laws)