If anyone's discussed this somewhere else, point me there, please. Maybe the Washington Post article on the result got posted to Hubski, but my efforts to find it here haven't been successful.
I think tribalism's wedding with anti-intellectualism (as others here have noted) has driven us to where we are currently. This is another part of "the equation". Quotations because we're dealing with human beings in a completely nonlinear system, and that's being optimistic, at this point.
TL;DR is Figure 3:
Maybe we should've heeded the two-party warning?
Yooo, I did a project on basically this in my social network analysis class last semester.
We analyzed the Senate via Senators who voted similarly on the same bill using publicly available data and built basically that Figure you linked (for the Senate). It was fun! Also terrifying!