I can assure you that communicating a threat to do harm to an individual or a group of individuals (either in person, or via some medium) was already illegal in every state in the Union, prior to the introduction of any legislation specific to terrorism.
It's called a "terrorist threat" in the context of attempting to terrorize a specific person.
Of course, I once changed my answering machine when I was getting a string of threats over my pro-life activities:
"Hi, I can't come to the phone. Do it at the beep. By the way, if you're calling to threaten me, I just got a new rifle from the gun store, would you be so kind as to ACT on your threats for once so I can boresight it?"