This is such a weird discussion. That Sanders harmed Clinton's campaign is obvious and he was wrong in doing so. That doesn't mean that there aren't other things Clinton should have done to win or whatever but given the closeness of the election it is probably true that she would have won had he not done the things he did.
And, to be clear, this isn't about him running in the primary. It's about the campaign strategy he picked, his refusal to drop out and refusal to concede his loss.
He conceded and endorsed her the week after she was cleared by FBI director Comey.
