Persuade the right? How do you persuade believers?
By having and delivering the better argument. Both sides have their true believers, but they are not the majority on either side. The battle is over the people that can be swayed with reason. The democrats lost this round.
No offense but I remain skeptical. I have yet to find a conservative who acknowledges that the US government has not a debt problem despite me citing various academic sources or explaining it in detail. The best I got so far was: "Ok, but..." with some "my gut tells me you are wrong"-alias afterwards.
Speaking for myself if the Democrats crashed and burned with Bernie I would not be sticking the knife in and twisting it right now. They would have at least had a candidate with some ethics and principles. Bernie probably regrets folding too easily for the DNC. I know I would have.
Bernie conceded when there was no sliver of a chance of him getting the nomination. Essentially one move before checkmate. And not endorsing Hillary would have helped the Democrats exactly how?