The Democrat party does not have common “mores,” “shared myths.” The party is a coalition of groups with different “mores,” “shared myths.” The Republican party is the same. Because of the dominance of the two parties, to have much influence you must register to one party or the other. Independents don't get to vote in primaries.

Each of the two parties will struggle with out internal unity. Total victory by any of factions within the party coalition will diminish the party leading to electoral losses. Some level of internal conflict is productive and unavoidable but too much conflict is destructive. Balance and a respect for differences is best. Best within both parties and across the aisle.