I'll tell you. It starts with throwing money at ±14 other candidates nobody has ever heard of but whose policy platforms spans the spectrum between the most conservative two candidates and the most progressive. Then the party collectively staggers the primary elections to the point where the progressive candidate can lead and win most of the initial states, but when the party finally comes around to the first state of a moderate size and one of the otherwise less popular conservative candidate suddenly inches ahead, the remaining no-name candidates suddenly drop out, throw their support (and delegates) behind him in a less-than-legal exchange for cabinet positions, so before a large portion of the country even gets a chance to vote, the progressive candidate is told to pull out because there is no possible way he can win enough delegates for the nomination.

When the Democrats say 'don't vote 3rd party because it will split the vote' -that's because they're projecting and it's exactly what they do to ensure a more conservative candidate wins the primary.