Clarence William Nelson II (born September 29, 1942) is an American attorney and politician who served as a United States Senator from Florida from 2001 to 2019. A member of the Democratic Party, he previously served in the Florida House of Representatives from 1972 to 1978 and in the United States House of Representatives from 1979 to 1991. In January 1986, he became the second sitting member of Congress to fly in space when he served as a payload specialist on the Space Shuttle Columbia. Before entering politics he served in the U.S. Army Reserve during the Vietnam War.Nelson retired from Congress in 1990 to run for Governor of Florida, but was unsuccessful. He was later appointed Treasurer, Insurance Commissioner and Fire Marshal of Florida, serving from 1995 to 2001. In 2000, Nelson was elected to the U.S. Senate seat that had been vacated by retiring Republican Senator Connie Mack III with 51% of the vote. He was reelected in 2006 with 60% of the vote and in 2012 with 55% of the vote. Nelson ran for a fourth term in 2018, but was narrowly defeated in the general election by then-Governor Rick Scott. In May 2019, Nelson was appointed to serve on NASA's advisory council.In the U.S. Senate, he was generally considered a centrist and a moderate Democrat. Nelson supported same-sex marriage, lowering taxes on lower and middle income families, expanding environmental programs and regulation, protecting the Affordable Care Act and expanding Medicaid.