tldr: The DNC argued in court that they have the right to rig their primaries, and in the end the courts sided with them: the DNC is legally entitled to rig their primaries
{ Jared Beck, the attorney representing Sanders supporters in the class action lawsuit [said this in court]
“People paid money in reliance on the understanding that the primary elections for the Democratic nominee—nominating process in 2016 were fair and impartial,” Beck said. “And that’s not just a bedrock assumption that we would assume just by virtue of the fact that we live in a democracy, and we assume that our elections are run in a fair and impartial manner. But that’s what the Democratic National Committee’s own charter says. It says it in black and white. And they can’t deny that.” He added, “Not only is it in the charter, but it was stated over and over again in the media by the Democratic National Committee’s employees, including Congresswoman Wassermann Schultz, that they were, in fact, acting in compliance with the charter. And they said it again and again, and we’ve cited several instances of that in the case.”
Later in the hearing, attorneys representing the DNC claim that the Democratic National Committee would be well within their rights to “go into back rooms like they used to and smoke cigars and pick the candidate that way.” By pushing the argument throughout the proceedings of this class action lawsuit, the Democratic National Committee is telling voters in a court of law that they see no enforceable obligation in having to run a fair and impartial primary election.
The DNC attorneys even go so far as to argue that the words “impartial” and “evenhanded”—used in the DNC Charter—can’t be interpreted by a court of law. Beck retorted, “I’m shocked to hear that we can’t define what it means to be evenhanded and impartial. If that were the case, we couldn’t have courts. I mean, that’s what courts do every day, is decide disputes in an evenhanded and impartial manner]
if you're wondering how the case turned out here's the wikipedia:
{ Their suit was dismissed by Judge William Zloch of the U.S. District Court for the Southern District of Florida for lack of standing.[1] The judge found that none of the plaintiffs had claimed to have donated to the DNC on the basis of promises contained in the DNC charter, and therefore the plaintiffs could not claim to have incurred damages.[1] The court held that "To the extent Plaintiffs wish to air their general grievances with the DNC or its candidate selection process, their redress is through the ballot box, the DNC’s internal workings, or their right of free speech — not through the judiciary." }