(Cheyenne, WY) â United States Attorney Mark A. Klaassen has announced his resignation from office effective midnight January 31, 2021.Upon his resignation, Klaassen will be taking a post with the State of Wyoming. Klaassen, a graduate of Notre Dame Law School, had previously served as Assistant United States Attorney for the Civil Division, and as Chief of Staff to the General Counsel for the United States Department of Homeland Security. He was nominated by President Trump on July 21, 2017, confirmed by the Senate on November 9, 2017, and sworn into office on November 21, 2017. During ...