Mike Huckabee could have won either time had he been the nominee. Mitt Romney was not viewed as more likeable than Obama. Huckabee is - and wouldn't have made those same gaffes that Romney made. Mitt Romney only had 4 years of being Governor. Obama had 4 years of being President. Mike Huckabee had nearly 10 years of being Governor, and before that, just less than 3 years of being the Lieutenant Governor - elected Arkansas' second Republican as Lieutenant Governor since reconstruction (in a special election in 1993 then [re-]elected to a full term the following year). The last Republican before him was elected in 1966 and served 1 term from 1967 to 1971. Huckabee then became Governor finishing an unexpired term and then elected Governor twice in his own right.
And to disagree with me about that would be to say that Brian Sandoval was unelectable as Governor in Nevada in 2010 because of the unpopularity of his predecessor Jim Gibbons.
You might then reply "Oh, well Brian Sandoval ran against him in the primary and beat him" and that is true. Brian Sandoval won that primary 55% to 27%.
Then comes to questions. Assuming third terms were allowed, and Bush were to seek it - considering his low unpopularity and America's foolish obsession with "electability" rather than standing up for ideals they believe in - he would have had other primary opponents that year and likely not been renominated.