You can be questioned by SS agents and hauled off to jail and possibly imprisoned for threatening the life of the president. If they can prove that a very high number of these nuts on social media actually go off, then I favor taking action against anybody directly threatening to kill other people on social media as this creep did.
As in " I'm going down to the school/office/factory etc. and start shooting people." I'm not talking about someone saying "if so and so harms my child or loved one, I'm going to kill them." That is an indirect threat or warning
At the very least have their weapons confiscated.