Once they declared it a terrorist organization (which is the problematic side of everything), they can claim these are unlawful combatants and do not have any of the protections of the Geneva convention, like any other war on terror assassination.

So I don't think double tapping is a war crime, any more than bombing a car with terrorists in the first place and that doesn't seem to be regarded internationally as a war crime. However, they could have done better to highlight Venezuela actual involvement with terrorism (which is real but not enough for this) rather than magically declare them terrorists just to not go through Congress

Just like Obama did

https://scholarship.law.ufl.edu/flr/vol69/iss1/7/

https://archive.is/ruphc