U.S. Air Force General Terrence J. O'Shaughnessy, commander of the North American Aerospace Defense Command and U.S. Northern Command, and Kirstjen Nielsen, Department of Homeland Security Secretary, discuss their complementary missions to protect and defend the United States during her visit to Peterson Air Force Base, Colorado, Sept. 6, 2018. (U.S. Air Force photo by Tech. Sgt. Joe Laws)