This is one of the best exchanges in yesterday's Kentucky Senate debate. When asked a straightforward question, Rand Paul cannot come right out and say Social Security and Medicare are unconstitutional, though he claims he "never said that".
He also reveals himself as a tenther, which by itself contradicts his claim that he doesn't want to see Medicare and Social Security abolished by Supreme Court reversals of established case law.
I'll bet someone can find a video or transcript where he does say Social Security and Medicare are unconstitutional. I'd be willing to lay odds on it.