Talking about the "Fair Tax" plan is playing with fire. Any candidate who expresses the slightest interest in the plan is immediately slammed with negative ads claiming he would put a 23% sales tax on top of every purchase.
I don't think the Fair Tax plan works, but if you're bound and determined to talk about it, then you'd better be able to nail your opponent's mischaracterization of it:
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I'm against the Fair Tax substantively and politically, but Rand Paul is still poised to win despite the backlash on this issue, so he must be doing something right.