Senator Byrd is a very good example of how somebody can successfully recover from the mistakes of his youth. He has said many times that he was wrong to join the Klan.
He was the longest serving member of the senate, he had earned respect not only of Senators (both Democratic and Republican), but he was respected in general in Washington as an elder statesman. When General Petraeus was nominated by Obama to serve in Afghanistan, the first thing he did was to visit Robert Byrd, as part of his confirmation process. As President Pro tem of the Senate, he was fourth in line for presidency (after VP and Speaker of the House).
In spite of the mistakes of his youth, Senator Byrd achieved greatness.