For some people, Ron Paul would be considered to have a "bad performance" regardless of what he says or how much support he gains.
Well, he has a tendency to seem like he's ranting: he goes on tangents that seem off-topic, he gets visibly over-excited when he talks about his favorite issues, and he refers to concepts and arguments that most debate viewers probably have no familiarity with. And his esoteric positions are bound to cause him trouble, no matter how well he can explain himself. Regardless of the merits of his positions, he sounds loopy to the uninitiated.
Paul is also really poorly endowed with regard to almost all of the superficial qualities that have been shown to influence voters (poor posture, waves his arms wildly when he talks, wispy stature, high pitched voice that frequently cracks, talks really fast). He'd perform better if he didn't suffer from these disadvantages.