Good article. I'm old enough to remember when American politics was less polarized. I think there are probably a large number of contributing reasons why it has become so hysterical. By hysterical, I don't mean funny.
First of all, the public has never been very well educated in civics or history. I don't know when those subjects became boring or hard or unfashionable. I remember as a very young kid when we moved to Wisconsin from Canada my parents being appalled it how little our new friends knew about a foreign country that was one hour's drive north. I don't want to to belabour the point, but Americans in general, for whatever reason, don't have much of a grounding in their own history beyond the big picture fairy tales they were fed in school. I was an A student in history in High School and it was super easy to be so, because the standards were so low.
The Vietnam War, the racial wars of the sixties, and the Watergate affair, tore apart the old social contracts and opened new divisions in between many, many groups. The young no longer trusted the old and vis a versa, Nixon was drummed out of office and the right never forgave the left for that.
The advent of the 24 hour news cycle ushered in the era of the screaming me-me's (to borrow a phrase from Spiro Agnew

). Today, it's very hard to find the news presented the way Cronkite and his contemperaries did. Journalistic integrity is a oxymoron this days. The sources of information are so many that it's hard to avoid tuning into the one you are most comfortable with. Most people I've observed, don't want to think outside their comfort zone. They want to hear news that does not challenge their world view.
Why is that? I think it comes back to the fact that real history and real civics are not taught in a way that makes it interesting. Independent thought is not encouraged, rote learning is still the dominant method and memorization is how you pass the tests. Too many kids think it's boring and uncool and find celebrity to be an easier and more interesting thing. So do their parents and I'm afraid it's a downward spiral. I'd guess that more people watch Big Brother and Survivor than all the primetime news shows put together.
Not that they all do. I spent two weeks hanging out with my daughter and her fourth year university friends in Montreal last year. I was so pleased to find out how well informed and interesting to talk to they were. Politics, art, history, sex, you name it, that house was in a content chatter about the world around them. Plus they didn't even own a TV. But I fear they are in the minority. Most twenty-two year olds are not like that. They sure weren't when I was twenty-two. Most of my friends from those years were and still are, dismally misinformed about the world around them.
So the CNN's Fox News, MSNBC's of the media pander to their demographic. It's all about holding on to their base and hopefully increasing it. Profit is the motive; it always was. But combine a undereducated, bored and lazy audience, with corporate machines that are more than happy to feed their fears, to the point of saturation, and you get folks who are ready to believe anything.