Robert Byrd- died June 28, 2010. A former member of the Klu Klux Klan. "Late in his life, Byrd explicitly renounced his earlier views favoring racial segregation.[56][57] Byrd said that he regretted filibustering and voting against the Civil Rights Act of 1964[58] and would change it if he had the opportunity. He said joining the KKK was "the greatest mistake I ever made."
David Duke- "ran in both Democrat and Republican presidential primaries, was openly involved in the leadership of the Ku Klux Klan."
Harry S. Truman- Democrat-alleged member of KKK
All the other prominent Democrats who were members of the Klan were so in the 1920's. 
Source: Wikipedia