"If Barack Obama becomes the president in November, again, I will either be dead or in jail by this time next year,"

I don't see that as stating an opinion by definition. Bill characterized it as an "almost threat". I suppose Nugent could turn around and say, "I meant that I would either kill myself in disgust, or get arrested for screwing a goat in front of the White House in protest". But he knows full well that that isn't what he was feeding his audience.
I think I've mentioned a personal situation from years ago here before. I had just moved to a new apartment in Chicago. A mental case on the same floor would come out in the hallway at all hours of the night and shout total nonsense. Then one night the rant was, "I'm going to kill someone, and they won't be able to do anything about it, because I have the power of God in me, and you can't mess with God." I never knew for a fact what the guy was actually capable of, but I went to the police. (As things turned out, relatives of the man came to visit by chance and they got him committed).

Nugent Probably doesn't have the guts to do anything but spew crap. But with a guy crazy enough to make that speech, who wants to take bets?