One thing the Republicans have done over the past couple of decades is increasingly polarize the electorate, and really put effort into the politics of hate. That's a popular strategy with totalitarian governments, because it gets people looking the direction you want them to (anywhere but at what you're actually doing).
It worked, as it usually does. Among other things, they pandered to what they call "values voters". The thing is, people on both "sides" of politics (an oversimplification if ever there was one) vote their values. The Republican fear-mongering grabbed a bit of the middle as well, and so it worked well - a die-hard core plus a good chunk of the ordinary everyday person, at the expense of the people who are less likely to vote for you will get you power - for a time.
But the problem is that the people they have upset the most are growing, while the people that they're relying on are both shrinking and abandoning(1) them(2) in revulsion(3). Young voters, in particular, are increasingly secular, and that's a problem for Republicans, because they have attacked the secular and their values at every turn.
The Republicans are beginning to reap what they have sown.
Blogger Nate at FiveThirtyEight talks about the problem McCain has with nonreligious voters.
The religious only slightly favour McCain over Obama. The nonreligious overwhelmingly favour Obama. As time goes on, unless the Republicans move toward the centre, they're going to increasingly lose the now-secularizing middle, and their history of vile attacks on them won't be quickly forgotten. If they do move toward the centre, they'll lose what remains of the right-wing evangelicals. Things are not looking good for the Republicans in the next 3 or 4 elections, unless they can completely reinvent themselves. I don't think they'll be able to do it.
They could stew for a generation in the cesspit they've dug for themselves - and they'll still stink less than they do now.