That's a massive topic.. I'll make a thread on it if you want to debate it.
But, here's the situation as briefly as possible.. it came out in the emails, DWS was discussing how to set up the primary schedule to favor HRC, so that before Bernie's message could get out there, she would open up a big delegate lead. Which she did during Super Tuesday 1. From there they just had to rig the NY and California primaries.. which was easy in NY.. it's a closed primary. They stripped something like 200,000 voters from the rolls in Brooklyn. If you look at the primary map. Bernie won every single county in New York, except NYC, where they sabotaged democracy. California they intentionally trained poll workers wrong, they trained them to give NPP voters provisional ballots instead of Democratic Crossover ballots, so NPP voters (independent voters) votes would not count, because Bernie won independents by wide margins. Going into the convention.. Neither candidate had enough delegates to win the nom so, they had to break Bernie's spirit somehow. I still don't know how they did that because you can't buy Bernie.
There's many other things, like closing polling stations to discourage participation, the chair throwing incident with Roberta Lange and Bernie people in Nevada, voting machines when audited having to subtract Bernie votes and add Hillary votes to match the reported totals..
But, the clearest piece of evidence is exit polls missed wildly in some cases off by +10 pt margins. When it came out that the exit polls were missing, they canceled exit polling for the remainder of the primary.
The methods ranged from propaganda to all out election fraud. But, they couldn't even admit that they favored HRC. all we heard from DWS, was I was fair. Everyone knew she wasn't. Most Bernie people I knew wouldn't of voted for HRC. They weren't into politics. Bernie was the only reason they wanted to vote.