I doubt there is some major Democrat establishment conspiracy, I don't think there was one in 2016, there's just lots and lots of stupidity and incompetence and hurt pride and laziness.
"The Myth Of Incompetence: DNC Scandals Are A Feature, Not A Bug"
https://medium.com/@caityjohnstone/the-myth-of-incompetence-dnc-scandals-are-a-feature-not-a-bug-4f264352d4f7There most certainly is a lot of stupidity, incompetence, hurt pride, and laziness in the DNC, but this is the perfect environment for the Democrat establishment to illicitly manipulate outcomes in the directions they desire, even if it is contrary to the wishes of their general voter base.
The 2016 election process showed pretty clearly there was a conspiracy to disenfranchise Bernie. Unfortunately he just bent over and spread his ass even wider rather than protesting it, and as a result, a lot of people who were voting Bernie are now voting Trump as a giant "FUCK YOU!" to the DNC.