WHAT?
How could you forget Mike Huckabee??
Anyway, if Obama is unpopular and turns out to be another Carter, then the Republicans will naturally go the way of Reagan and nominate Huckabee (who like Reagan was second in the primaries during a Democrat year).
If Obama is popular, then they will nominate Giuliani or Palin as a "throwaway card" so as to not damage candidates like Huckabee who actually have a chance in 2016.
Anyway, I predict the former situation. So, Huckabee is the nominee, wins the election and becomes the new Reagan.