I'm not totally sure this is true of America to be honest (the existence of a distinct left and right - not the fucked up bit)
Now I accept that the 'political compass' isn't the last word in this, and it is by any honest measure a subjective index, but it illustrates the incredibly narrow choice corridor quite well. Draw vertical lines between Trump and Clinton, and the gap between them is your left/ right spectrum. America's much cherished 'freedom' is pretty much a freedom to conform
https://www.politicalcompass.org/uselection2016
The way I like to look at it as that the American political landscape has been dominated for the last 50 years by a giant unbalanced pendulum. This pendulum swings 2 pts to the right and then swings 1pt back to the left. If you repeat this over enough cycles you end up with Trump, and you're also well on your way to electing fascism (which I'm not convinced is a contradiction in terms)
For the Republicans this possibly started in the last 60's with Nixon pushing back against the so-called 'counter culture' although you might trace it back further into the paleo cons. At this time the Democrats were still fielding candidates like Humphrey and McGovern who had some connections with traditional supporting blocs in social organisations and labour unions. Carter momentarily flipped this mood when he won an election by virtue of not being Gerald Ford, but that didn't last long. Reagan would go onto beat Carter in 1980, and the Democrats fielded and lost with Mondale and Dukakis there after. The epicentre of American politics was changing, and the Overton window was migrating right. Eventually as we went into the 90's the Democrats began their own transition as their own candidates became increasingly more and more right wing. You can almost see this as a perfect linear regression. This of course legitimises the Republicans and they can push onto the extremes of the window even further. It's probably reached a point now whereby if their patron saint, (Ronald O'Reagan) were to stand today, he wouldn't win the nomination (gun control alone would stop him)
I think the important take out though is that Trump needn't be a freak. He actually represents America much more than many Americans are comfortable about admitting. I actually get a bit tired listening to all the Democrats bleating that he only 46% of the popular vote and she got 48%. So what. The point is he was a disqualifying candidate who still managed to get 46% of the vote. Even if he had lost, this should still be of a massive concern. Western Europe's most right wing country is France, and we tend to get a bit spooked when the FN can manage 40%. OK some of the outliers in eastern Europe like Poland and Hungary bear comparison with America, but America is pretty way out there now, and needn't be finished just yet. Trump might not be the worst of what they're capable of electing. Ultimately if the rest of the country continues to elect alt-right quasi militarists against the wishes of the wealth producing states of coastal areas, you do wonder if the fabric of the union will hold together, and whether perhaps a federated system might come to pass as Yankee land and California look for greater autonomy? Who knows