Larison makes a good point:
Were [Huckabee] somehow nominated and elected, this would not ultimately herald the movement of the GOP in a more populist direction, but would set the stage for internecine GOP warfare as conservatives would turn against him quickly and seek to oust him as progressives tried to do with Carter. The Carter parallels are already overused, I know, but they seem eerily appropriate.
A case in point: This morning's Lisa Schiffren post on Huckabee, which might as well have been titled "Go Back to Dogpatch, You Stupid Hillbilly!"
It's interesting, in this vein, to compare Huckabee's '08 insurgency with McCain's '00 outsider campaign for the GOP nomination. There are parallels: Both men made enemies of the supply-side wing of the party, and both found one of their strongest constituencies in the liberal media (though in Huck's case, the honeymoon may be coming to an end). And then there are differences: McCain's anti-establishment run had a large cheering section among the right-wing pundit class, whereas Huckabee's emphatically does not; McCain found votes among old-fashioned fiscal conservatives, moderates and independents while making an enemy of the Christian Right, whereas Huckabee's base is the Christian Right; and McCain was facing an establishment unified around a single candidate, whereas Huckabee's attempting an insurgency in a fractured party. Essentially, the McCain strategy was to leverage an ad hoc coalition of moderates and neoconservatives to take down the candidate favored by all the party's interest groups; whereas Huckabee is trying to exploit divisions between the party's interest groups, and ride one of those groups - the social conservatives - to victory.
Overall, I would say that McCain circa 2000 was a stronger (and better prepared) insurgent candidate in a host of ways than Huckabee circa 2008 - but Huckabee is running through a broken field, which makes a big difference.