The DNCs own charter and bylaws grants anyone running as a Democrat equal treatment in accordance with their own rules. Sanders doesn't call himself a Democrat because he's more progressive than the Democratic party, not because he's less..
There's Sanders sitting all the way to the left of the American political spectrum, then Warren, then the Democratic party, then people like Hillary Clinton, Nancy Pelosi, & Chuck Schumer, then the Republican party, and finally people like Ted Cruz, Donald Trump, & Lindsay Graham
He chose to register as a Democrat because there are inherent flaws within the two party system that prevent 3rd party candidates from doing as well. When was the last time one did "well"? Perot? Nader? Never gaining more than something like 21% and being blamed for Bush (in Nader's case). People propose the idea that Sanders should have run as an Independent, just like people propose the idea that Sanders should just start his own party, as a way to dismiss him. It's not a serious solution. It's a way for them to say "Don't disrupt the status quo!" and serves as an easy scapegoat if their candidate eventually loses. They can just blame the 3rd party candidate and claim they split the vote.
That's not how it works in America. You're never going to catch a savvy American politician, especially one as entrenched in politics as Hillary Clinton, red handed with the money bag in their hands. Instead what you see are subordinates colluding with mainstream media outlets, invites and attendees to private political dinners, kid gloves when it comes to questioning their political agenda, but fierce opposition towards their opponents. What we do have evidence of is consistent with this. So it's a bit disingenuous to ask to see a specific politician caught in a specific act when they've designed the laws and their own political strategies in a way specifically to avoid it.
If Clinton speaking directly to the head of MSNBC in order to get them to go softer on their coverage of her is corruption/collusion, so is the head of the DNC doing the exact same thing. If Clinton devising the idea to question her opponents religion before a primary specifically in order to garner more votes against him is corruption/collusion, so is the DNC communications director doing the exact same thing.
People/organizations acting in a way specifically to benefit Hillary Clinton is corruption/collusion whether Hillary Clinton herself had any role in it or not. It's clear her campaign did, it's clear the DNC did, it's clear multiple mainstream media outlets, including CNN, MSNBC, Vox, Washington Post, NYT, and others did.
This is you attempting to justify it. Hillary Clinton herself said she regretted it, same with Donna Brazile. They wouldn't have said that if it was based on nothing, hearsay, or conjecture
I cited their own charter and bylaws that state otherwise. Where does it say that the DNC is to subvert democracy in the Democratic primary in favor of the candidate they (the Democratic establishment) support? I wonder why the Democratic National Committee even has a charter and bylaws that say they're to remain neutral among candidates if they can just choose to ignore them in favor of whoever they want? I wonder if Democrats would donate to them if they told them their vote didn't actually matter, that the leadership could just choose to select the candidate in a smoke filled back room if they wanted to?
I know I wouldn't. That's not why I donate to political candidates/parties
He would have split the Democratic vote, people like you would have blamed him for Trump. The way he did it eliminates that option and forces you to accept the candidate Democrats pushed was terrible and couldn't beat the most disliked opponent in American history. Had he ran as an Independent and lost, it would have lended(lended?!) leant much more credibility to the idea that Clinton didn't win because of him. He knows that.