I think we need to ease up on Bernie and his campaign here. I seriously doubt they were trying to supress votes in Puerto Rico with their request to cut polling locations.
What is much more likely, particularly given Hillary's landslide win, is that he was simply unable to find enough volunteers to fill the slots needed to observe at all the polling locations. He didn’t have enough enthusiastic support on the island to find people willing to be present at the vote counting.
This isn’t a question of character, just one of competence. We should be careful about those kinds of accusations. Leave the conspiracy theories and lies about vote rigging to the other side.
His stunningly dishonest response, though, is probably a different matter.