It is so easy to debunk all these claims too. It's crazy they are trying to get away with it. I hope the Clinton campaign hits back soon. Seriously, all you have to do is check Byrds wiki and you can find this:

For the 2003–2004 session, the National Association for the Advancement of Colored People (NAACP)[64] rated Byrd's voting record as being 100% in line with the N.A.A.C.P.'s position on the thirty-three Senate bills they evaluated. Sixteen other senators received that rating. In June 2005, Byrd proposed an additional $10,000,000 in federal funding for the Martin Luther King, Jr. National Memorial in Washington, D.C., remarking that, "With the passage of time, we have come to learn that his Dream was the American Dream, and few ever expressed it more eloquently."