Once the Dem "leaders" (DW Schulz et al) failed to heed the evident passion behind Bernie and decided pre-primary to push Clinton forward by whatever means, no matter how dishonest, they were doomed. We can't let some geezer with millions of passionate followers upstage someone, no matter how worn out, who for decades had been the rethuglicans' favorite punching bag - when it was her turn!?
The Dem party beat itself using the same corrupt practices that Trump then used to beat them.
Hillary got more votes and more superdelegates. By a significant margin.
Bernie was a modern-day carpetbagger using the DNC to run for POTUS when he'd done nothing for the organization and had even hurt it in the past. Hillary, as a Democrat, had been First Lady, a Senator, and Secretary of State. She supported the party and raised a metric fuck-ton of money for it.
Of course the DNC was going to support Hillary. It should have supported Hillary. Her record of loyalty to the party, public service, and support warranted that support.
Then a bunch of goddam purity-testing Bernie Bros decided to either stay home, vote third party, or vote for Trump out of spite. The latter is fitting I suppose as that what Trump supporters seem to have primarily voted on: spite.
Well, they showed us, didn't they. Now Trump is POTUS because Bernie Supporters and third party voters just have too much goddamn integrity. That's a goddamn joke.