Look for the most nasty internecine primary fights in both parties in living memory. Both parties face the same demographic splits in mirror. Each party has a hardcore group of outsiders at odds with party leadership on philosophy, priorities, and the general conduct of the party. In neither party does there appear any interest on the part of leadership or the grassroots/outsider contingent to accommodate the other faction. It is not merely a fight over issues, it is a personal struggle for control and political survival in each party. No one is interested in playing along for the good of the party, because all four relevant factions are convinced that allowing the other faction to gain power is equivalent to party and personal destruction.
This Fivethirtyeight.com piece analyzes the surprise upset in the W. Va Dem primary, and how it follows the trend of upsets among Rs in Utah, and other anti-incumbent trends.