At his New York Times blog, Paul Krugman has some fun with what he calls "the crazy lower bound," arguing that while there's a continuum of crazy throughout the political spectrum, there's a "bunching" of crazy on the right-wing that's unlike anything else.
[Y]ou might expect the views of US politicians to be spread along a smooth left-right continuum — and that it indeed what you find if you look at the center and left of US politics. On the right, however, there certainly seems to be a lot of bunching right at a sort of crazy lower bound — there are a lot of politicians just as crazy as Ted Cruz, but very few who are (or at least are willing to be seen as) crazier than Ted Cruz. It’s a lot like the distribution of wage changes, where there is a spread of positive changes but a large spike at zero and very few actual wage cuts.
Krugman doesn't offer any concrete theories as to why there's the Cruz crazy lower bound; he just insists that folks shouldn't be so quick to dismiss the usefulness of the left-right political model for judging the crazy. "[W]e really do have a pretty one-dimensional political universe," he writes.