Not all speech is protected in all contexts. Death threats to the President might not be strictly illegal, but they'll get you in a bunch of trouble nonetheless. Like slander and "fighting words", some speech carries consequences that push it out from under the safety umbrella of the 1A.
It's like the saying, "You can ignore reality, but you can't escape the consequences of ignoring reality." So, yeah, "You can say that, but you can't escape the consequences of saying it."
I remember when BO was first running for POTUS and a girl from one of his call banks sent the SS to a woman, in TX, I think, because she said she would never vote for anyone advocating for the murder of unborn children.
The woman was shaken to the core over the visit from the SS and the questioning - she had made no threats, nothing - the call bank worker was just a punk who wanted to make a point with a woman because she wasn’t voting for BO.
I hope this man is called on the carpet - watch what the school does as well.