I suspect I know what the answer is, but I am not *entirely* sure just why Miserable Failure George Bush had his approval rating plunge into the 20s. The "fever" didn't break, of course, it just went briefly into remission and then came roaring back at 108 degrees. His approval rating cratered long before the mortgage/financial/economic crisis hit, so it wasn't that.
I *suspect* the answer is that "they," generally, stopped pushing the rage injection button on a daily basis. They began again for the 2008 election but Bush was already in the past.
The lesson is, never stop turning the rage button up to 11. Their voters are just anger junkies.