Sadly, it's not Bannon or Trump or the Murdochs or Tucker or any other singular figure/corporation that are to blame for the massively polarized, us-versus-them, tribal sentiment among Republicans and Democrats - nor for the anti-science, conspiracy theory laden, nationalistic, racist attitudes among a segment of Republican voters.
It's a confluence of factors that are to blame. The chief among them, I think, is gerrymandering (other factors contribute to this too such as the lack of action among Democrats to improve the well-being of rural Americans in the face of loss of jobs due to overseas competition - and so on).
Gerrymandering - the drawing of voting districts to favor one party or another - leads to polarized politics - since voters in any gerrymandered district are predominately either Republican or Democrat - any candidate wanting to win election must perforce appeal to a polarized electorate. Middle ground candidates, expressing the desire to compromise, have virtually no chance of winning in such gerrymandered districts.
Too, there's a widespread resentment among many/most? rural Americans of the so-called elitist left. And a distrust of most news outlets. And a distrust of science. And a resentment towards immigrants.
Anecdotally - my father - Chemical Engineering MSc and PhD Mathematician - but born and raised in Missouri - loved the TV show, "All In The Family."
"All In The Family" featured an over-the-top right-wing nutjob - Archie Bunker - who continuously expressed the most outrageous of right wing positions. It was obvious irony.
But you know what?... The irony sailed completely over my father's head - he loved Archie and agreed 100% with the bullshit he professed.
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And that to me is the root of the problem - a vast swath of Americans adore Archie Bunker. Trump is but a current manifestation of their beliefs. And when Trump is gone, due to the Internet and rapid free exchange of ideas - some new Archie Bunker/Donald Trump figure will emerge, and will be adored by the Right. And divisive politics will continue.
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Until such time as gerrymandering is eliminated - and thus that political candidates must cater to a diverse set of opinions to win office - until then - there is no such thing as the "United" States: we're a nation divided.