- John Randolph Thune (/ˈθuːn/ THOON; born January 7, 1961) is an American politician serving as the senior United States senator from South Dakota, a seat he has held since 2005. A member of the Republican Party, he will become the Senate majority leader and Senate Republican leader in January 2025. Thune is in his fourth Senate term and is the Senate minority whip, a post he has held since 2021, and is the dean of South Dakota’s congressional delegation. He served three terms as the U.S. representative for South Dakota’s at-large congressional district from 1997 to 2003.