https://ivn.us/dnc-to-court-we-are-a-private-corporation-with-no-obligation-to-follow-our-rules/

In the case Wilding vs DNC in 2016 the DNC argued that they have no duty at all to run a fair primary. DNC attorneys argued that the organization is a private political corporation with the right to select its nominees internally and that statements of neutrality were general political or aspirational remarks rather than legally binding contracts.

Spiva (DNC lawyer) stated in court: “We could have voluntarily decided that, ‘Look, we’re gonna go into back rooms like they used to and smoke cigars and pick the candidate that way.’ That’s not the way it was done. But they could have.”

The DNC won that case. The judge said, "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."