You are absolutely correct in your point, and I have experienced this dynamic many times. I describe it to my wife as the leaders of the group wanting to have the sandbox to themselves to play in. The point of this post was whether the national party skewed the results toward Sanders as has been argued, and there is really no evidence to support that claim. Despite this fact, the claim continues to be made, damaging our democratic (both small d and big D) institutions, just as Trump does with his attacks on the media and electoral process.