I think the Conservative wing of American politics is on the verge of a severe identity crisis, very similar to what the Liberals went through about 15 years ago. At the moment, far from being a coherent whole, the Republican party is split into at least four different factions:
1) The Rockefellers: As I blogged before, this group is close to being an endangered species. They lost the original GOP civil war to Ronald Reagan and the more fundamentalist right in the 1980s. The Rockefellers are fiscally conservative, but socially moderate. Their numbers are steadily decreasing as they are the polar opposite of the current predominant GOP group, the Fundamentalists.
2) The Fundamentalists: This group is currently in control of the GOP leadership. It is very socially conservative, but unlike traditional Republicans it is far less concerned with fiscal moderation. The Fundamentalists sprang out of the populists in the south and west that used to vote predominantly Democratic. This group was economically akin to the Democrats in terms of spending, but far to its right on social issues. While the type of spending the Fundamentalists prefer is very different than that of the populists (being more focused on the rich and corporations), the character of the populism movement is still present in their support for giant farm subsidies and pork projects.
3) The Traditionalists: This group is economically and socially quite conservative. Personified by Senators John McCain and Chuck Hagel, it is the most recent group to display friction with the GOP leadership. Unlike the Rockefellers and Libertarians, it still has a reasonably strong following, and has gained the advantage recently by being seen as "straight-talkers." If a viable challenge does break out to the Fundamentalists, it will probably come from this group, with support from the remaining Rockefellers.
4) The Libertarians: Traditionally, this group has been the most isolated from GOP power circles, representing "extreme Rockefellers" in a sense. Many Libertarians are faced with an identity crisis at the moment, as the Democratic party (with its new found love-affair with fiscal discpline) is closer to their views on both social and economic policy. Unless the Republican party changes course soon, they could bolt en masse.
And if that wasn't enough, three of these four groups are internally divided on the merits of Neo-Conservatism vs. Isolationism (the Libertarians are pretty solidly isolationist, with the exception of a strong support of free trade)!
At the moment, the Republican party is still united behind President Bush (though we've seen chinks in that armor, McCain and the Rockefellers have started to find their voice again to protest certain Bush policies). If President Bush wins this election, the Fundamentalists will have enough of a mandate to maintain control of the Republican party. If he loses though, then a vicious internal party spate could develop.
The New York Times had an interesting article on the growing fissures within the Conservative movement.