He won't likely make that particular mistake. But there are so many ways to pratfall. I like how he's claiming that medication from his back surgery caused that flub.
Here's what I think caused that flub: Perry and his ilk like to run around enumerating all the government agencies they'll close. (By the way, he was naming cabinet departments, not agencies, so there's that.) Typically, they haven't bothered to work out the details of how the functions performed by that department would be carried on. Perry was campaigning in eliminating Depts of Commerce, Education and ... what was it again ... Energy. Why couldn't he remember Dept of Energy? Because he hadn't given two seconds of thought as to why he would eliminate the Dept of Energy (or the other 2) and how which of their functions would be eliminated entirely or transferred to other areas of government. It's policy by jingoism. It's very shallow, and thus easily forgotten, even by its proponents.