I agree. Targeted assassinations of US citizens are a violation of the 14th Amendment, as is a law allowing indefinite detainment of US citizens without any kind of due process.
And whether it is illegal or not, it is absolutely crazy to define as a terrorist somebody who is “belligerent”, without defining “belligerence” in any way. It’s also crazy to allow that determination to be made by any one person, with no means for scrutiny.
So what’s the solution?