My understanding is that Bernie supporters sued the DNC after the 2016 election for DNC rigging the election against Bernie. DNC admitted to doing it in court and said that they had every right to do whatever they wanted because the DNC is a private business. The judge sided with the DNC and dismissed the case. I'll try to dig up an article on it. If I find it, I'll edit to add.

edit: Not the article I was looking for, but it'll do: https://caityjohnstone.medium.com/the-dnc-fraud-lawsuit-has-been-dismissed-dismiss-the-democratic-party-7413e4de0b43

My understanding is that Bernie supporters sued the DNC after the 2016 election for DNC rigging the election against Bernie. DNC admitted to doing it in court and said that they had every right to do whatever they wanted because the DNC is a private business. The judge sided with the DNC. I'll try to dig up an article on it. If I find it, I'll edit to add.