The Geneva convention only limits the treatment of combatants in the military service of a foreign government. For example, you must use full metal jacket bullets to shoot them.
But there are no limitations on what a state can do to its own inhabitants, thus they use hollow point bullets against US citizens.
Likewise, agreements pertaining to the use of nuclear, chemical and biological weapons only apply when used against persons outside of a state's territory. There is no restriction against using them WITHIN one's territories, except for nuclear test bans. So you can't TEST them against your own people, but you can USE them against your own people.
So Joe Biden is well within his rights to state that he can nuke Americans he deems to be a threat.
The whole point of "domestic terrorism" labels is so that certain persons or groups can be designated as "domestic terrorists" and thereby bypass the Bill of Rights and deploy unlimited force and tactics against them.
Nobody was complaining under Bush when people were getting disappeared, extraordinary rendition was done to take them to other countries for purposes of torture. That was done by labeling them terrorists.
People who survived this process COULD NOT SUE. They could not sue because in order to do so, discovery would have to include information that is classified and would compromise "national security". Therefore, no suits are possible. The case law is all there.
So anyone, or group of people, designated as terrorists can be treated in an extra-constitutional manner -- ex. nuked, gassed, tortured or whatever -- and there is no standing to even complain.
So now, WHO are the designated terrorists?
MAGA people, Q people, pro-white people, etc.
Thank goodness a Republican administration put this into law!