In this blog, I want to focus only on a few, not all, of its implications.
If a president of the U.S. has a power to assassinate American citizens, then, logically, this means that he also has punitive powers that stop short of killing, since killing is for most of us just about the worst thing that can be done to us. In particular, if he has the assassination power, then he also has the power to imprison you indefinitely, to torture you, to starve you, to isolate you from the company of others, to take away all your property, to prevent you from working, to remove your vital organs, and to mutilate you. If a president has a power to kill you, then he has the power to do anything he wishes with you and to you.
In addition, a presidential power to kill renders all laws or agreements, domestic and international, that forbid ill-treatment of prisoners inoperative, for if a president has a power to kill, then he has a power to stop short of killing you. He has a power to capture you and then treat you any way that he pleases.
I am using here only the notion of a fortiori. It is that if a man can run a marathon of 26 miles, then with greater reason or more strongly, we conclude that he can run 1 mile.
Even prior to this power to kill comes the power to designate someone as a terrorist or some organization as a terrorist organization, thereby allowing powers to be pressed against them. This power to designate also runs right up against due process.