"We’ve already said it’s not ok for the mentally unstable to possess firearms and that clearly doesn’t work."  -- Um, you know that "saying" something doesn't make it law, statute, or federal law, right?
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What legal statute do you know of that elected officials are pressing and debating to preclude mentally sick individuals from access to firearms?  Which of these laws are being shut down by the NRA?  Your Gabriel Giffords talking points are beyond debunked.