LSU has the only shot to do so, otherwise, and I never thought I would say this, but Mizzou in the SEC Championship. Alabama's defense isn't "great". Its good though, its just that nobody on their schedule has a decent offense so far, besides TAMU and they exploited them pretty good.
I think Auburn could definitely beat Bama. And if Bama slips one more time after that there is no way anybody will give them consideration for a Natty Title. And there will be two unbeaten teams by years end. I believe it will be Oregon and FSU.