Means different things to different people. I don't take it as an insult, I don't know why anyone would. NY Times ran a front page above the fold story calling Carlson an American Nationalist, that's the basis of my meme.
You're on the internet and could easily look it up. According to The Stanford Encyclopedia of Philosophy it "indicates the aspects that characterize and distinguish the United States as an autonomous political community. The term often serves to explain efforts to reinforce its national identity and self-determination within their national and international affairs".
Hope that helps.
