My favorite polarization scholar is Nancy Bermeo who views polarization as an elite-led process. I think that is particularly important to consider when answering the question, are American voters polarized? Yes, but that could easily be rectified by more responsible political leadership, and that is where the need for proportional representation enters the picture. If you haven't already, you should check out the report from Scott Mainwaring for Protect Democracy on proportional representation in the House of Representatives.
Nice, I would add, though, that the 1960 APSA report on "responsible parties" was also a significant contributor to current polarization. The idea of Dixiecrats and Rippon Repubs seemed confusing and "irresponsible" to the experts. They wanted the parties to be entirely sorted/purified. That might be useful in a multi-party system, but here it has led to visceral hatred. https://www.3-16am.co.uk/articles/sam-rosenfeld-the-polarizers-postwar-architects-of-our-partisan-era?c=a-hornbook-of-democracy-book-reviews
My favorite polarization scholar is Nancy Bermeo who views polarization as an elite-led process. I think that is particularly important to consider when answering the question, are American voters polarized? Yes, but that could easily be rectified by more responsible political leadership, and that is where the need for proportional representation enters the picture. If you haven't already, you should check out the report from Scott Mainwaring for Protect Democracy on proportional representation in the House of Representatives.