Mitt Romney is an incredibly vulnerable Republican candidate, from his numerous policy reversals to his championing of the Massachusetts health care law that served as the basis from Obamacare. But for him to lose, somebody else has to beat him. And like Tim Pawlenty before him, Texas Gov. Rick Perry is blowing his chances to exploit Romney’s weaknesses.

The defining moment in this debate may well have been the point at which Perry went on the attack against Romney for being a flip flopper. As I noted earlier, there’s a long file to choose from. And Perry had clearly rehearsed such an attack – you can tell he was starting to go through the list of issues Romney had reversed on, and even used the “for it before he was against” phrasing, a not-so-subtle reference to the infamous Massachusetts flip flopper, Sen. John Kerry. But the exchange came toward the end of the debate, and as has been his habit, Perry began to fade as the debate wore on. During this particular answer, he wrestled for words and stammered. He couldn’t finish his sentences. If you weren’t a political junkie who knew all of the background, you’d have no idea what Perry was mumbling about. And Romney’s smooth response made him come off as more steady and reassuring, even though on substance, Perry should have owned him.