Michael Joseph "Mike" Mansfield (March 16, 1903 – October 5, 2001) was an American politician and diplomat. A member of the Democratic Party, he served as a U.S. Representative (1943–1953) and a U.S. Senator (1953–1977) from Montana. He was the longest-serving Senate Majority Leader, serving from 1961 to 1977. During his tenure, he shepherded Great Society programs through the Senate and strongly opposed the Vietnam War.After retiring from the Senate, Mansfield served as U.S.