How is Mccarthy's statement a non sequitur? A non-sequitur, by definition, is an inference that does not follow from the premises. Didn't he pretty much state that they created the Benghazi committee to go after Hillary and, because of that, her numbers are dropping?

Even though I think that it was a stupid and careless statement, I do not think that is what he said. He said that her numbers are dropping because of all the scandals that she is involved in (including Benghazi) and that he is happy about that. It does not necessarily imply that this is the reason that the committee was created.