Reply #8: The question is more about whether it is legal for the government to apply the laws of war against

[BzaDem]

an individual, organization, Justin Bieber, AFSCME, etc (not about an abstract declaration).

The truth is that those in the US, the US Constitution (and applicable Constitutional law) applies. So the laws of war generally cannot be applied.

As for non-US citizens overseas, international law governs (as well as domestic law constraints on the President's power). So if you were to make an argument that the US government cannot apply the laws of war in dealing with an organization that declared war, you would need to support that by pointing out the piece of international law that says so, or a piece of domestic law/case law that prevents the President from authorizing force.