Honestly, I'm not happy with Rand Paul's vote to approve Chuck Hagel as Secretary of Defense. I was pretty hopeful after he voted against cloture (i.e. he voted to continue the filibuster) despite 18 other Republicans voting to end debate, effectively enabling the approval of Chuck Hagel. But I knew that he said repeatedly that he believes that Presidents have a right to have the political appointees of their choice and his vote doesn't really depend on agreeing with the nominee. He did vote for John Kerry as Secretary of State and he probably agrees with him even less.
I don't think this is a fatal blow but the good Senator did damage his brand today, causing many of the people who he has convinced that he is not like his father to rethink their support of him. I think though that as long as he remains the tip of the spear, fighting government largesse and foreign aid to enemies of the United States, that people will forgive one vote, especially one as meaningless as the approval vote (the cloture vote was the key vote and he voted the right way there). This vote may still haunt him though in the 2016 primaries.