On July 11, 2007, Nobel Peace Prize laureate Betty Williams gave the keynote speech to the International Women’s Peace Conference in Dallas, Texas, and said (to laughter and applause from the audience):
“I mean right now, I could kill George Bush, no problem. No, I don’t mean that. I mean — how could you nonviolently kill somebody? I would love to be able to do that.”
So, according to this article - all we need to do is file a complaint in federal court, and the SS will necessarily arrest the individuals in question, else they will necessarily need to drop charges against this man.
His poem is offensive, but not illegal or threatening.