The truth here is more fuzzy. It should concern all of us that Hillary was able to 'loan' the DNC money, and receive what amounted to a veto, over specific candidates for specific positions in the Democratic party administration. Staff members in the DNC really ought to be trained that offering up some 'suggestions' on how the Kentucky party can best sabotage Sanders with some hit ads before their primary, is probably not a real comforting that the playing field at the home office is neutral.
That being said, Sanders was responsible for sander's loss. When you lose more votes, more open and closed primaries, more pledged delegates, more unpledged delegate, and you lose in virtually every economic and regional demographic to your opponent, you have serious weaknesses as a candidate that were plenty exploitable by anyone. Sanders could not for the life of him win over blacks, older voters, Hispanics, moderates, women voters, then his problem was a lot bigger than some emails and spats with the DNC.