Biden/Trump/Whoever is president could simply officially order one of his top officers to push a button that drops a hellfire missile on their political opponent and then pardon them. The President is the commander-in-chief of the armed forces and also has the executive privilege of pardon available to them at their discretion for any reason or no reason at all. I'm 100% sure the president will find somebody in the chain of command with morals flexible enough to obey such an order.

And since you can't go after the man himself because a corrupt SCOTUS is apparently poised to rule that they have immunity for "official acts" which is a nebulously defined term that can apply to literally any heinous act that they want, the country has essentially created a king by proxy.