IMO, to whatever extent more folks are disaffected with the GOP, it has to do with the economic collapse and the light in which this collapse casts certain aspects of conservative views on government, regulation, and so on.

Actually, it occurs to me that the Republicans, and conservatism more generally, have a built-in disadvantage. If you boil conservatism down to its bare essence, all it really means is to preserve as much of tradition and the status quo as possible, for as long as possible – or, as many conservatives themselves often like to put it, to stand in front of history and yell “Stop!” If that’s all you’re interested in doing, is it any wonder you wouldn’t have many promising new ideas? Indeed, by introducing new ideas you would, by definition, cease to be conservative. (That wouldn’t make you liberal, mind you, but rather something neither here nor there.) That is conservatism’s big, inherent, immutable Achilles’ heel. Of course, it also means that if you’re unable to flag down history, you end up as road pizza. That sounds like a good, concise description of the current state of the GOP to me.

http://grammar.about.com/od/classicessays/a/cornponetwain.htm