Don't ask a question that (1) you don't want the answer to, and (2) they've already answered.
This is exactly the perilous road many folks around here discussed when SCOTUS issued its "the President has absolute immunity for everything he does" decision. All he has to do is make any act he takes be colorably within the scope of his duties (and hey, "execution and enforcement of our laws" sounds pretty colorable), and he has absolute immunity. Seriously. Even if the basis is on the "outer perimeter" of his powers, he has a presumption of immunity, and the only way it can be overcome is to show that the act was purely (as in entirely, 100%) private in nature. But because functionally everything the POTUS does, outside of golfing, is at least tangentially within the scope of his powers and duties, that exception is meaningless.
So, all we need is an internal memo declaring Macanudo to be an active terrorist threat against the United States, he sends a Hellfire missile into your AMC Pacer as you're driving the Sonic one day, and he has 100%, complete and total immunity. Note that the designation of you as a terrorist doesn't have to be accurate. It really doesn't even have to be rational or defensible. The very act of designating you as such is a discretionary call within the scope of his duties, and thus....total immunity. Ironically, if he ordered you arrested, you'd have some protections: writ of habeas corpus, all that stuff. But if he just skips all that, and kills you....he is worry-free. He has total immunity.
This is the end-game. The president has the power to kill anyone -- and that necessarily means EVERYONE -- and he is not answerable for that at all.