If you were to take Barack Obama back in time maybe 15 or 20 years and call him a Republican, people would have hardly noticed. Considering the fact that "Obamacare" and a health insurance mandate were both pushed by Republicans and the Heritage Foundation back in the 1990's, aside from his stance on gay marriage, I'd say there are few differences between Obama now and many of the mainstream Republicans of the 90's.
However, go to any Tea Party rally and you'll inevitably find people with misspelled signs proclaiming him to be a "socialist, fascist, communist, Marxist", etc. Back in the 1990's, before the media outlet known as Fox News was on every retirement community center's TVs, there were many Republicans who could care less about what people did with their bodies. They also sometimes supported reasonable restrictions on guns and didn't mind reaching across the aisle to get things done because it was either right for the country, or for their collective pocketbooks.
Most of them are gone now. They've either died, been replaced by the shrieking maniacs of the hard right, or switched parties. I remember in 1993 when Virginia elected George Allen as governor by a wide margin, yet the GOP lieutenant governor candidate (Mike Farris) lost by 9 points even though the election went heavily to the GOP. Mike Farris was one of the wacko "Quiverfull" homeschooling folks and he fits in with the likes of Michele Bachmann and Rick Santorum today. Back then the moderates of the party, like John Warner, refused to support him. They would rather a moderate Democrat win than allow someone they correctly viewed as "too radical". I remember the furious sense of betrayal and resentment from nutty fundamentalist homeschoolers who grudgingly peeled their "Mike Farris for Lieutenant Governor" stickers off their minivans after the election. They actually disliked George Allen because they thought he wasn't conservative enough, believe it or not.
Since those days, politicians like George Allen have tacked their sails ever further into the breeze that pushes the party ever harder towards the hardline right. Principle and soft corruption have been replaced by outright corruption and corporate ownership, as well as the never-ending contest to prove who is the most ideologically pure. While the showmanship involved in ideological posturing endears them to the radical base who they can count on to show up for primaries and elections, it makes them unelectable overall. Back then, you could get the support of the rightwing by making racial remarks in an assumed private setting or promising to pass a bill to teach creationism in school without worrying about being caught on a cellphone video. Many of these people still run campaigns that way, and cater to the radical base for the primaries, then wonder why they get laughed at when they try to tack to the center and still lose in the general election.
There's still centrist people left, they've just allowed their more intellectual arguments for being Republican be drowned out by the shrill dog whistles and "you betcha" booksellers and pundits for almost a decade now. I remember watching William F. Buckley at an early age and while he was very conservative, he actually made his argument with points that took more than 10 seconds, a wink, a hairflip and a catchphrase to get across.
I believe the rumors that after Romney gets his ass handed to him on November 6th, 2012 that the GOP top brass will finally realize they can no longer cater to the hard right in primaries and expect to win elections, hoping that their remarks weren't caught on tape to be used in ads in October and November. I think Chris Christie is one of those politicians who knows that his future and his path to the White House lies in the middle and not on the fringe, which is why he didn't play the partisan game when it came to Hurricane Sandy. I think he, and the powers that be, have realized that obstructionist tactics and continued pandering to angry old white people is a losing bet in the long run. Gauging by the remarks I've seen on social media in the last couple days in response to his embrace of Obama, there's definitely some people who have lost their damn minds over it.
Perhaps they've realized, finally, that they've lost a younger generation (myself included) to the Democrats by catering to the old Bible thumpers and the last of the pre-segregation Dixiecrats rolling around The Villages or Scottsdale in their golf carts. Maybe they've come to terms with the fact that angry old white people will be pushing up daisies within the next decade or so and that they will need to find someone else to cater to. Maybe they've realized that a generation that embraces multi-culturalism and overall tolerance is so far out of their reach right now, that they'll wake the fuck up. Maybe they've finally grasped that people like Sarah Palin and "awwww shucks" jingoistic patriotism doesn't attract the emerging demographic, unlike the current dying one that has been stuck in the left lane, with their blinker on, for the last 20 years.