It is now known that the Russian government hacked the e-mail accounts of the Democratic National Committee (DNC), and then turned those hacked accounts over to Wikileaks's -- and Wikileaks then did Russia's bidding by releasing them to the public. It was done to hurt the candidacy of Hillary Clinton (who Putin did not like) and help the candidacy of Donald Trump (who Putin does like).
The inference was that the DNC was somehow rigging the primary election to favor Hillary Clinton over Bernie Sanders. While some silly things were said by some not-too-bright people working for the DNC in those e-mails, there was (and still is) no proof that the DNC did anything to aid Clinton or hurt Sanders.
Sadly, many of the Bernie supporters decided they didn't need any actual proof. They needed an excuse as to why their candidate was losing in the primaries, so they jumped on the Russian hacking as though it proved more than it actually did. They accused the DNC of rigging the primaries, and Clinton of doing all sorts of crooked things. And too many of them are still telling those same lies today -- lies based on inferences drawn from the Russian hacking.
To be blunt, they were duped by Vladimir Putin and his horde of hackers into vilifying the only candidate with a chance to defeat Donald Trump (Putin's choice for president). I doubt they'll admit it, but they were played like a fiddle and happily danced to Putin's tune. They should be ashamed of themselves.