Clarence William "Bill" Nelson (born September 29, 1942) is the senior U.S. Senator from Florida. Nelson is a member of the Democratic Party. Nelson became the second sitting member of the United States Congress to fly in space when he flew aboard the Space Shuttle Columbia as a Payload Specialist during NASA mission STS-61-C (January 12–18, 1986). Bill Nelson lives in the Baldwin Park neighborhood of Orlando (as does Republican Senator Mel Martinez) and Washington.
Nelson married Grace Cavert in 1972; they have two children: Bill Nelson, Jr. and Nan Ellen Nelson.
In 1986, Nelson became the second sitting member of Congress (and the first from the House) to travel into space. He went through NASA training, along with Senator Jake Garn of Utah. He was a Payload Specialist on Space Shuttle Columbia's STS-61-C mission from January 12–18. Ten days after his return, on January 28, 1986, the Space Shuttle Challenger exploded shortly after lift-off. Nelson was originally scheduled to be on the Challenger flight that resulted in the destruction of the Challenger and the loss of the entire crew, but a scheduling conflict bumped him to an earlier launch.
From 1995 to 2000, Nelson was the Treasurer and Insurance Commissioner of Florida.
He has voted against the Partial-Birth Abortion Ban Act as it had no exception for the life or health of the mother.
He has also voted against a bill providing for criminal penalties for anyone harming an unborn child during the commission of a crime.
In general, Nelson has high ratings from other left-of-center political action groups. 
Nelson has also introduced legislation banning paperless electronic voting machines 
In 2007, the Senate Intelligence Committee voted on a measure to de-fund torture by the CIA except in "dire emergencies." Nelson was the lone Democrat to vote against the measure, but all Republicans voted against it as well, thus defeating it 
Senator Nelson is also a member of the Congressional Cuba Democracy Caucus
He is widely regarded as a Moderate.
Nelson's job approval ratings were 49 percent during the 2006 campaign, three percentage points higher than fellow Florida senator Mel Martinez, a Republican in a nominally red state.
Republican Rep. Katherine Harris won the Republican primary, and faced Nelson in the November general election. In an interview with Sean Hannity on March 15, 2006, Harris claimed that Nelson was a member of the ideological far-left and had taken bribes. She did not state from whom, nor did she give any other specifics as to these allegations. Nelson is generally regarded as a moderate in Florida.
James Dobson promised to launch a battle "from sea to shining sea" against Nelson's reelection if he participated in a filibuster of Bush's pro-government court nominees. Dobson has been joined by other activists, such as Randall Terry, because of his opposition to Samuel Alito and his refusal to join what were largely Republican efforts to block the removal of Terri Schiavo's feeding tube. The Schiavo incident prompted Brian Darling, a strategist in Mel Martinez's staff, to write the Schiavo memo that articulated a plan to use the Schiavo controversy as a campaign tool against Nelson in 2006. Darling resigned when it was traced to him, and Martinez apologized publicly to Nelson. 
Nelson was reelected as Senator on November 7, 2006 with 60 percent of the vote. His victory is the largest margin by a Democratic candidate in the state in many years.
This change was in violation of the Democratic National Committee's rules regarding state primary dates, which caused DNC Chairman Howard Dean to threaten to strip the state of its delegates to the Democratic National Convention if they did not schedule the primary for a date that fell within the DNC's guidelines. Senator Nelson has been playing an active role in attempting to restore the delegates, going so far as to threaten a lawsuit against the DNC if an appropriate settlement is not reached.
On May 31, 2008 the DNC bylaws committee decided to seat all of the Florida delegates with each being apportioned one-half vote.