Steve Benen used the weekly research 2000 poll to make a graph. A reader recently made a very interesting reference. He said he believed that the GOP was morphing into the American equivalent of the Parti Quebecois. It is essentially a regional party now - representing the South in the national discourse. And its rhetoric seems divorced from any desire to actually hold responsible public office. So Republicans, like the Quebecers, tend to use politics as a means for disruption or protest or threat or veto.
It's also worth remembering that the huge amount of noise on the far right is actually quite narrowly based. Here's a fact from the Time profile of Beck:
In 1987 comedian David Brenner bombed in syndication with about 2.5 million viewers at midnight which is roughly what Fox, the leading network for political talk shows, averages in prime time.
There is certainly a very angry far right base out there. But it would be foolish to over-estimate it.