Senator Hillary Rodham Clinton, 59, is in her second term representing New York state. She was first elected to the U.S. Senate in 2000. She is the wife of former President Bill Clinton and the first First Lady elected to public office.

John Edwards, 53, was elected to the U.S. Senate from North Carolina in 1998. He served for one term. After an unsuccessful bid for Vice President and President in 2004, he worked as the director of a new Center on Poverty, Work, and Opportunity at the University of North Carolina at Chapel Hill.

Mike Gravel, 76, represented Alaska in the U.S. Senate from 1969 to 1980. He played a key role in the release the Pentagon Papers, the secret government documents pertaining to the Vietnam War. In 1971, he successfully blocked an attempt by the Nixon Administration to renew the military draft.

Senator Barack Obama, 45, is the third African American since Reconstruction to be elected to the U.S. Senate. After serving in the Illinois state Senate from 1997 to 2004, he was elected to the U.S. Senate in 2004. He earned his law degree from Harvard in 1991, where he became the first African-American president of the Harvard Law Review. He delivered the keynote address at the 2004 Democratic National Convention.