Well there's another issue here: the "public figure" rule.
The NRA as a group would probably qualify, and if so the standards for how much opinion you can throw at them is broader.
You can actually say much worse things about, say, Donald Trump and get away with it than you can saying stuff about your neighbor down the street. The courts basically say "Donald has put himself in the public arena, he's going to have to toughen up".
Very likely the same would be said about the NRA.