IMO not just a crime. I’m no lawyer, but to me it seems like that satisfies all three of the conditions in the definition in the US Code (18 US Code 2331) of “domestic terrorism”.
(5) the term “domestic terrorism” means activities that—
(A) involve acts dangerous to human life that are a violation of the criminal laws of the United States or of any State;
(B) appear to be intended—
(i) to intimidate or coerce a civilian population;
(ii) to influence the policy of a government by intimidation or coercion; or
(iii) to affect the conduct of a government by mass destruction, assassination, or kidnapping; and
( C) occur primarily within the territorial jurisdiction of the United States.
Condition C is obvious. Jones made his statement while inside the United States.
Condition B, you could make a case for either i or ii applying depending on whether Mueller is a civilian or officially a member of the government during his tenure as special prosecutor. A death threat is certainly intimidating!
Condition A seems like it would have the most wiggle room for Jones. “I didn’t really mean I wanted to kill him, it was a joke!” But I bet a lawyer could argue that issuing a death threat is “dangerous to human life” even if not acted upon, especially if they could show that Jones’s followers have taken his jokes as suggestions to be acted upon in the past.
