How did the Grand Old Party of Lincoln, William F. Buckley Jr, Rockefeller and Barry Goldwater turn into the party of Sarah Palin, Rush Limbaugh and Mitt Romney?
Longer than I have time to discuss now but the short answer is the Party turned South. That helped them for a while but there isn't a Republican on the horizon who can unify the disparate versions of conservatism (social, neo-con, big business, libertarian, traditionalist, etc..) And the social conservatives make noise in direct inverse to their power but they scare off independents and energize the other side.
The interesting part to me is that whoever wins this election, Obama or Romney, will lead a country where somewhere between 45-50% of the population HATES him and thinks he's illegitimate.