Well they are learning what those who are GOP voters have learned for years now, that the Dems have made it a fine art with “voter fraud”.
I think that Bernie is a MUCH better campaigner than anyone gives him credit for. He lets his supporters deal with this, while he stays above it. He didn’t want to get involved with the email crimes. Why should he? Others will do it for him. He is always polite and gracious. He could give Republicans some lessons.
Of course, this doesn’t change the fact that he is almost entirely wrong in his approach to every issue...but still. Credit where credit is due.