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."