I think Perry attempted to compensate for his poor debating skills by acting overly assertive and tough. I don’t think he is a jerk at all, but he has come off that way. It just hasn’t played well. Never let anyone say debates don’t matter. Perry is a perfect example of someone who’s fortunes collapsed with bad debate performances, and Cain has had just the opposite experience with his “happy warrior” debate style.
Now, why. Well, the essence of charisma is a sense of totally authentic conviction, without any internal ambivalence or conflict. I give you Ronald Reagan as an example of a man with deep convictions and without self-doubt, and you see the result. Herman Cain has some of it, which is why he thrives, despite rookie stumbles and fumbles--he comes across as real.
Perry comes across as studied--forming his own positions as he goes along. And the people sense it. Example: if he is so shot with the flat tax, why didn't he introduce it months ago? Answer: because he really doesn't give a shit, but realized that if he didn't come up with something, Cain and even Romney would steal the issue. So he heaved one up. Sorry, no sale.