It would be Slander, since it was spoken word.
There are 4 basic standards for winning a Slander/Libel case.
1)Someone actually DID say/write it.
2)Someone other than the plaintiff heard/saw it.
3)It can be proved who said/wrote it.
4)The Plaintiff's finances/reputation were damaged by what was said/written.
The first 3, in this case, are a slam dunk.
Number 4 is tough to prove. Almost impossible in very many cases. You'd practically need someone to testify that, because of that statement, they didn't join or dropped membership from the NRA, or some similar action, to prove it. Tough to do. It's like proving that the reason I've never met a person is because the person doesn't like me, but I don't even know the person exists because I've never met them.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.