To answer only the question asked of Rub-a-Dub, I believe it has to do with the national parties. The national parties have become the true power in the U.S. If a politician wants to get elected he or she must worship at the feet of the party leaders and by party leaders I do not refer to a single elected official.
Locally where I live if a person wants to get elected to office he or she must kiss the ring of the party leaders. If the party leaders believe a candidate will be a faithful and obedient puppet for the party, that candidate will receive the endorsement of every club, elected official, as well as receive generous campaign fund contributions. At any time an elected official poses a perceived threat to a party leader, the party will run 2 strong candidates against them in the primary.
In ancient times the religious elite pulled the strings of kings and emperors. Political parties have replaced religions in the U.S. I can't think of a better example of this than the 2016 DNC National Convention in which the DNC rejected the party members' decision and went with Hillary over Sanders.