Although I understand where they are coming from and them not liking Hillary, personally I think they are cutting their noses off to spite their faces and many of them are just exceptionally arrogant and taking the moral high ground. They could, in theory, bring Trump to the White House, possibly not now with his huge unfavourable ratings, but that doesn't matter to them, they would feel the same if his favourability was high. The statement they aim to make doesn't involve Trump at all, it wouldn't matter if it was Mickey Mouse running, they would take the same stance, and I feel it is completely counter productive and actually exceedingly destructive. I'm glad Bernie has sat down with Hillary and agreed to work with her to take down Trump, but a fair few of his supporters need taking down a proverbial peg or two as well.