It is estimated 10-15% of Sanders voters voted for Trump or third party candidates in Wisconsin, Michigan and Pennsylvania. Hillary Clinton lost those states by a total of 77,000 votes. Nobody in the party believes Sanders worked hard to heal the wounds of a very difficult primary. Certainly not as hard as Clinton did to heal the party after her loss to Obama. Many have long memories.
Hillary ran a dumb, entitled campaign against Cheeto. She's ultimately to blame for her loss. But at the same time, Bernie's Bros and Bro-ettes had an effect on the outcome. I'm not sure there's ever been quite that many primary Dem voters who swapped sides, at least in my political lifetime.
Oh, yeah. Go Joe! Dump Trump!