He's absolutely a terrorist according to 18 USC 2331:

(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.

His explicitly stated goal was to affect the conduct of the government and coerce the civilian population via mass destruction.