in his view, the NRA is full of a bunch of racist OFWGs, just like the KKK.
Right, and therein lies the difference. If he'd said, "the NRA is controlled and funded by the KKK," that would qualify. To say "the NRA is like
the KKK" would not. The first is a blatantly untrue statement; the second is an expression of opinion.
Just because something is hurtful or ignorant doesn't mean it qualifies as defamation. If it did, I'd truly fear for the 1st Amendment.
Dumb people have the right to say dumb things so the rest of us have the right to say ain't dumb things.