Immunity here means declare whatever you want, and then mandate that the military eliminate anyone who opposes your new mandate. This “fun” hypothetical is a president invalidating their immunity powers and then having that decree reinforced by death, that second part is the illegal you want in this equation.
It’s done to “Save America”, so it’s an official act.
"If a president couldn’t freely do rapes, bribes, frauds and incite violence without repercussions, who would way to be president?"
one of the two candidates for US President probably