How are these comments by Ted Nugent a threat against Obama?

Could someone please explain to me why Ted's comment represents a threat to Obama? From Mediaite:

Ted Nugent’s remarks about President Obama at the annual National Rifle Association convention in St. Louis have earned him a follow-up conversation with the Secret Service. On Sunday, the singer remarked that “if Barack Obama becomes the president in November again, I will be either be dead or in jail by this time next year.” The Secret Service, which investigates all threats against the President, confirmed to New York Magazine’s Daily Intel blog that they have in fact flagged Nugent’s comment. “We are aware of it, and we’ll conduct an appropriate follow up,” the agent told the magazine. . . .