Why would Sanders supporters believe Hillary is playing dirty?
"Blumenthal was obsessed with the "whitey tape," and so were the Clintons, who not only believed that it existed but felt that there was a chance it might emerge in time to save Hillary. "They've got a tape, they've got a tape," she told her aides excitedly."
"Clinton's staff was surprised; Ayers hadn't been part of her prep. But Hillary had a number of friendsamong them Sid Blumenthal, whose nickname was "Grassy Knoll"regularly feeding her on the sly negative tidbits of dubious veracity about Obama. (In getting ready for that night, Hillary casually mentioned to her aides that she'd heard that Obama's mother was a communist.)"
It was the old Bill-Hillary-Sidney gang who handed over the weapons of defamation to the Republicans in the closing stages of the last campaign, and it was they who were not-so-secretly upset when the candidate of their own party actually won.
http://www.slate.com/articles/news_and_politics/fighting_words/2010/01/loose_lips_or_dirty_tricks.html