His diplomatic experience included negotiations on military basing in Asia, the Cambodia peace process, and the Five-power talks on arms transfer restraint. Lewis led the U.S. delegation to the Wassenaar Arrangement Experts Group for advanced civil and military technologies. He was also assigned to the U.S. Southern Command for Just Cause, the U.S. Central Command for Desert Shield, to the National Security Council and the U.S. Central American Task Force. At Commerce, he was responsible for policy and regulation affecting, satellites, high-performance computers, and encryption. He was the Department lead for the Select Committee on U.S. National Security and Military/Commercial Concerns with the People's Republic of China. Lewis served as Rapporteur for the 2010, 2013, and 2015 UN Group of Government Experts on Information Security.