Most CTH readers are aware the RNC and DNC are literally private clubs with the ability to do anything they want regarding rules & by-laws inside their respective organizations.  As such both republicans and democrats can do whatever they want to determine their candidate. Understanding this opaque process was one of the cornerstones to figuring out how the RNC controlled the nominee outcome in 2012 and their failed attempt in 2016.
Here’s an interesting perspective on the likely DNC nominee looking at the procedural processes within the 2020 democrat national committee rule changes.  No super-delegates (in round one) and no winner-take-all rules for state delegation distribution.

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Despite the challenges to scour through the details of party rules and regulations, it would be nice if more media spent time on this aspect of elections. Ultimately it is the club rules, and the candidate’s ability to use or overcome those rules, that is the best predictor of who will succeed in the nomination process.