> And there's plenty of precedent for that.
There is clearly precedent for criminally charging US citizens for such things, or in the case where they're either subject to the UCMJ or otherwise acting as a lawful uniformed combatant, maybe a court martial.
But what is the precedent for allowing unilateral lethal military targeting of known US citizens outside the US, or anyone within the US, outside of moments when the accused is actively engaging in physical violent warfare? I'm not aware of any before 9/11.
one would think that a formal declaration of war (at least minimally specifying who the US is at war with) would be needed otherwise anybody can be killed just under umbrella of "War on Terror" or "War on Drugs" or "War on Littering and Jaywalking"...
The legal existence of a war has established rules in US law, and a Congressional declaration is one way they happen (though not exclusive what you probably mean by a “formal declaration of war”, which suggests magic words).
> otherwise anybody can be killed just under umbrella of "War on Terror" or "War on Drugs" or "War on Littering and Jaywalking"...
The War on Terror has a legal declaration, which is expressly conditioned only on Presidential determinations, so requiring declarations doesn't actually meaningfully prevent that scenario when Congress is feeling lazy.
The grandparent post is a single sentence and identifies two instances that answer that question (they aren't a full answer because there are more examples in that timeframe.)
No, the logic is that the US government may target enemies in war by all the means lawful against enemies inwar, even if those enemies are US citizens, anywhere in the world, including within the US.
And there's plenty of precedent for that.
There may be good reasons given the nature and mechanisms of modern warfare to establish some additional limits on that now, but we can't have the discussion effectively if we start with a false premise about the rationale and the false idea that prosecuting war without special limitations when some of the individual enemy combatants are citizens is novel.
> I wonder if POTUS has to at least sign all the kill orders.
In general, no, the President is not required to personally sign orders to kill enemies in war, regardless of their citizenship.