One theory is that Americans have lost so many of the identity anchors they used to have (social and service clubs, stable jobs, churches, neighborhoods, ethnic subcultures) that political tribalism has begun to fill those gaps in their lives and the corollary to that is that the purpose of political discourse shifts away from dialect debate that reaches for consensus and solution, to where it is mostly directed at tribal membership declaration and maintenance, where the point is no longer to engage with contrary views at all.