Russel, now vice president for international security and diplomacy at the Asia Society Policy Institute, said Xi would not allow himself to “be reduced to the status of a mere guest celebrating the triumph of a foreign leader — the U.S. president, no less.”
US law about threats make no distinction in regards to the target so if the threat is credible enough or made often enough you’ll receive a visit from the FBI.
The modifier here is that it’s pretty hard for your average person living in the United States to make a credible threat against a world leader in a far away country.