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The secretly filmed video in which Mitt Romney appeared to disparage the 47% of Americans who do not pay income tax, was nothing compared to the harsh, divisive language used by some US politicians, radio hosts and bloggers. How did US politics become so polarised?

It was day one of our new life in America. I had arrived to take up my BBC reporting job and my wife and I were bringing our bags from the car. Our new neighbours showed up with cakes and soda. And a warning: "You'll want to re-park your car."

Eh? We had parked outside our picket-fenced new home and thought no more about it. But we had parked facing the opposite direction of traffic. This, in the capital city of the land of the free, is a violation. In Washington, you must park facing the same way as the cars are heading. It is safer, they reason, because you don't have cars nosing out into oncoming stream of vehicles. And my freedom? Fuggedaboutit.

The hatreds are ideological as well - some Americans don't see us as having basic obligations to our fellow citizens Prof Michael Slote, University of Miami

America, a nation we associate with rugged individualism, is actually - at least in its suburban guise - a nation of rules and conformity, a nation of community spirit, enforced where necessary by law. You may not say and do what you like in America, whatever the constitution says. You are expected to play nice. And you are all - every American - "in this together".

So what on earth has gone wrong? Why did Mitt Romney tell those wealthy donors, in the secretly filmed interaction that leaked out this week, that nearly half the nation were of little interest to him?

Never mind the poor politics - how can that be American? It feels so utterly wrong. But Mr Romney was being pretty mild when you look at the totality of the hatred - and that is not too strong a word - that the political classes in modern America throw at each other.

A miserable example comes on my car radio. We are somewhere in the middle of Florida, driving through a tropical rainstorm and a voice is booming out telling me that his opponent in their local congressional race "has benefited personally" from the bank bailout scheme set up in the wake of the financial crisis, "and so has his family!" Basically he's accusing his opponent of being a thief.

And this bile matters. It has real consequences. It leads, in Congress, to deadlock. A nation beset with urgent issues to confront - of which the size of the national debt is probably the most serious - cannot find the cross-party consensus necessary to act.

So here is the big question - a bigger question, frankly, than who is going to win this presidential election... What went wrong? And how can it be fixed?

I have been hearing three theories from Americans from across the political spectrum.

At the end of that rain-soaked journey, I landed at the coastal home of the Florida-based writer and newspaper columnist Carl Hiaasen. He made an interesting point about the sheer number of sources of information on offer to the average American in the digital age. The TV of course, and the radio, but also from the net the blogs and the YouTube video and the snippets of half noticed opinion on Twitter and Facebook. A maelstrom of fact and opinion and sheer nonsense. All mixed up.

Image caption Carl Hiaasen (right): It's getting harder to see the other point of view

Hiaasen feels for his fellow citizens.

"The ability to twist and fabricate makes it so much more difficult to sort through what's true and not true. You need to dig twice as hard."

In these circumstances, no wonder many people defend themselves with the obvious human psychological defence mechanism - they believe what backs up what they already think and disregard the rest!

And more than that, they get angry that with all this so-called information that seems to them to back up their own views, how annoying is it that other folks do not see things the same way? The crush of "facts" actually reduces people's ability to see the other point of view.

Michael Slote, Professor of Ethics at the University of Miami, agrees. But he wonders as well if there is not a deeper issue - an issue that goes to the heart of what it really means to be an American.

Image caption Joyce Kaufman: "I want to be banned from Britain!"

He sees that community spirit I identified at the start of this piece as a diminishing quality of American-ness. In fact, he believes it was a recent aberration. The real America is a tougher place, a place where bullying politics is part of the scenery.

He is depressed by what he sees as a nation reverting to type after a period of gentleness - brought on originally by the Depression and the New Deal politics that came after it - which suggested to Americans that in good economic times they could afford to help each other out.

"There is less to go around now. Less room for compromise," he says. "But the hatreds are ideological as well. Some Americans don't see us as having basic obligations to our fellow citizens."

I hope they sort it out. When you talk to individuals here you meet so many who are public-spirited.

The conservative talk show host Joyce Kaufman - who has been in trouble before for incendiary comments about immigration and guns - claims, I think with real justification, to be a backer of all Americans at heart. Even if it went socialist? "Yep," she says. "I don't have to stay if I don't like it here."

And she has a sense of humour. As we were leaving after interviewing her she takes me to one side; "I want to be banned from Britain, then I will feel I have arrived!"

Now that is proper American talk.

Justin Webb, a former BBC North America editor, is a presenter of Radio 4's Today programme. His television report can be seen on Newsnight, at 22:30 BST on BBC Two.