Since the end of WWII, the US has had, on average maybe 70 deaths/year due to terrorism.
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In that same time period, the US has had substantially more gun deaths than the entire death toll of all of America's wars, put together.
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Osama bin Ladin and AQ?  Amateurs.
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The NRA are so practiced at it, they have been able to prevent governments from even mustering the willpower even to try to take any realistic steps to prevent future attacks.  They have successfully intimidated the Congress and the state legislatures.  What other terrorist group has anything like that power?
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Yes, the NRA is, by several orders of magnitude, the largest enabler of murder, armed mayhem, and terrorism in America.
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Except that those bodies, though just as dead, and just as loved by the grieving families, don't get counted as terrorism.
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The NRA is, without question, the largest enabler of terrorism in America.
No other group is anywhere close.