Well, he's actually entered the race, at no small cost to his reputation and family. So that shows "fire in the belly".
If you think a politician is going to take a bribe to take a dive in an election, nothing anybody says to you is going to change your mind, especially when there is absolutely no evidence backing up your belief.
You might as well ask how anybody could be sure Sarah Palin wouldn't get in the race, win the nomination, and then decide the attacks on her family and the cost were just way too high, and resign. There is about as much evidence for that as there is for your "concern", and I would treat them with equal disdain.
I’m not talking about fire in the belly to win political office.
I’m talking about a very different kind of fire in the belly.
And I don’t think he will necessarily take a bribe. But I don’t have the trust in Perry that I have in Palin, based on their records.
And I would guess there are plenty of multi-billionaires out there who would pay a hefty sum if they thought it would give Obama a second term.