I don't wholly agree with either of these graphics, but at least the one I posted conveys the idea that "left, right & center" in the US is a discussion located mostly to the right of center in the context of the rest of the world.
The US is a mature state and there are plenty of safeguards against radical ideologies from the bottom. The problem we encounter is when extreme ideologies are pushed from the top, usually via proxy. The latest iteration of this is the Koch brothers and their ilk. The ideology these guys are pushing is essentially a return to feudalism. And they aren't just talking about it, they are doing all they can behind the scenes to make it happen. Their efforts include funding several influential think tanks and starting/funding the so called Tea Party. They won't stop until the US is reduced to Third World status. Meanwhile, other countries in the world, in particular China, aren't exactly holding themselves back in their efforts to catch up with and exceed the United States in every conceivable metric.