First lets talk about killing sinners. This question is well answered in the Summa Theologiae. (http://www.newadvent.org/summa/3064.htm Article Two) There's really not much for me to say here, it's laid out very simply and clearly. "God sometimes slays sinners forthwith in order to deliver the good" This sums it up, it is lawful to slay sinners who are causing grievous harm to good people.
However, according to Article Three, you can can not personally put the grievous sinner to death, because you do not have public authority to care for the body. "It is lawful for any private individual to do anything for the common good, provided it harm nobody: but if it be harmful to some other, it cannot be done, except by virtue of the judgment of the person to whom it pertains to decide what is to be taken from the parts for the welfare of the whole."
So we can't kill the wicked doctor privately, and our government will do nothing to protect its people from him, so maybe what we need is war. According to Article One of http://www.newadvent.org/summa/3040.htm, we again need public authority to wage this war in the first place. "For it is not the business of a private individual to declare war, because he can seek for redress of his rights from the tribunal of his superior".
Well, we can't really form a paramilitary group and burn Babylon, can we, because a paramilitary group was not entrusted with the Authority to make decisions for the public. So I guess what's left is a coupe of the current standing authority. Trump could disregard congress, start making decisions, and become defacto dictator, but unfortunately he'll never do that. So what we need is a public figure within congress, the White-house, etc, to march on Washington as Mussolini did, and be declared the dictator by Trump him self.