Your history conveniently stops at around 1970 and leaves our figures like Jerry Falwell and Nixon’s southern strategy. The partisanship is not being driven by rhetoric - it’s being driven by tens of millions of people being left behind by neoliberalism with zero attempt at mitigating the harm done. If people felt like the current system worked for them then they wouldn’t adopt extreme views.
But sure let’s keep on liberalizing and consolidating economic and political power. It’s worked out great the last 4 decades.
Edit because you edited: wanted to drive home point I can barely stand the democrats. In a sane country they would be the center right party