After the Veep and Speaker of the House if I remember 7th grade Civics class?
I believe that line of succession is correct.
I don't think, if Heller is involved, that it has anything to do with presidential aspirations. I think it would have to do about something "for the security of the Nation" as Logan was talking to Henderson about. These DoD types take their role in protecting and securing the Nation very seriously.
Though, you have to wonder how leaking nerve agent into hundreds of thousands of citizens homes, hoping that Jack Bauer could save the day in time, could be a something that would secure our place in the world.