So, I view Christie as the most electable and he most plausible from what I can tell. As an expert, my rating is zero on a scale of ten. I just express my thoughts here, I don't take sides except when te topic is narrow and specific and I feel that I have something useful to contribute.
IMHO the 2008 election was for or against Bush. His term slid into the election like sewage draining downhill. I doubt any Republican could have won in 2008. In 2012, the GOP self-destructed or they could have won. Romney was a dubious choice who made one error after another during the campaign. He wasn't a "bad man", just a "poor choice", and that had little to do with his "moderation".