The GOP wasn't always this crazy. Minnesota's Arne Carlson, for example, wasn't a bad governor. Schwarzenegger had his moments.
Ok, so the modern GOP has never been all that impressive. Still, it wasn't 97% insane until the mid-90s.
So what happened?
I don't think it's the rise of corporate America or the amazing concentration of American wealth. The former impacts both parties, and not all the ultra-wealthy are crazy. These trends make the GOP dully malign, but the craziness of Koch brothers ought to be mitigated by better informed greed.
That leaves voters. So why have a substantial fraction, maybe 20%, of Americans shifted to the delusional side of the sanity spectrum? It's not just 9/11 -- this started before that, though it's easy to underestimate how badly bin Laden hurt the US. It can't be just economic distress -- Gingrich and GWB rose to power in relatively good times.
What's changed for the GOP's core of north-euro Americans (aka non-Hispanic "white" or NEA)?
Demographics is probably a bigger factor. I can't find any good references (help?) but given overall population data I am pretty sure this population is aging quickly. A good fraction of the core of the GOP is experiencing the joys of entropic brains (here I speak from personal white-north-euro-middle-age experience). More importantly, as Talking Points describes, this group is feeling the beginning of the end of its tribal power. My son's junior high graduating class wasn't merely minority NEA, it was small minority NEA.
This is going to get worse before it gets better. The GOP is going to explore new realms of crazy before it finds a new power base; either as a rebuilt GOP or a new party.
It's a whitewater world.
Update 7/8/11: Coincidentally, 538 provides some data on GOP craziness ....
... Until fairly recently, about half of the people who voted Republican for Congress (not all of whom are registered Republicans) identified themselves as conservative, and the other half as moderate or, less commonly, liberal. But lately the ratio has been skewing: in last year’s elections, 67 percent of those who voted Republican said they were conservative, up from 58 percent two years earlier and 48 percent ten years ago.
This might seem counterintuitive. Didn’t the Republicans win a sweeping victory last year? They did, but it had mostly to do with changes in turnout. Whereas in 2008, conservatives made up 34 percent of those who cast ballots, that number shot up to 42 percent last year...
... the enthusiasm gap did not so much divide Republicans from Democrats; rather, it divided conservative Republicans from everyone else. According to the Pew data, while 64 percent of all Republicans and Republican-leaning independents identify as conservative, the figure rises to 73 percent for those who actually voted in 2010...