IIRC, specifically threatening the life of the President has never been held to be protected speech. For that matter, fighting words in general I think are held apart as a category - you can't go up to someone and be like "So hey, I'm gonna break into your house and murder you in your sleep," or similar, and then tell the police you were just exercising your First Amendment rights.
I'll grant as there's a space between a story about murdering the current President of the United States, and a specific threat to murder the President of the United States, but this does seem to be toeing that line just about as hard as it can be be toed.
