I could write a whole article like I always do on this, but I want to leave this an open-ended discussion for ya'll.
Here's why I think this could be the case: There's a few notable trends going on in American life under the surface in modern times. Religiosity is down, and interfaith marriage is up. Interracial marriage is climbing every year for the 3 biggest races in the US, and racial tension, while flaring up again if it isn't over-represented by the news, is certainly in long-term decline from the civil rights movement and black panther days. At least between black and white people, perhaps the Hispanic divide is increasing? But interestingly, political polarization is on the incline, and interpolitical marriage is dropping in approval. There's studies recently that shows that the identification as liberal or conservative influences how people view others more than their actual views, showing the importance people put to these identities.
In addition, with the global connection to Europe from the internet, the "American Civil Religion" (wikipedia it) has less respect in the modern era, with the American democracy being viewed as one of many and the current president not being viewed with much respect at all. Institutions are increasingly viewed as not internationally extraordinary but deeply flawed and not worth revering without reform. Even American concepts outside the government like the American Dream are looked at with a more cynical eye.
So here's my question: Are the old cohesive identities in the US of race, religion, and the core american identity in decline in favor of partisan identities? And if so, does that actually mean anything with how people interact with the state and each other? Or have I underrepresented identification with other facets of society like urban vs rural (notably more 50-50 than most countries) or class.