Feels to me like centrist left and right are getting pulled apart from one another to their respective ideological fringes.

This has pretty much just totally happened to the Republicans; Democrats have done a better job of staying centered and responsible, but I don't think that's a given forever.

> Something that seems absent these days in American political discourse is the assumption that the other party, in general, has a similar north start to your own

Well, they don't have similar "north stars" or visions of the country or normative values. But this isn't discussed or debated directly by anyone, politician, talking head, or otherwise.