I’m not a lawyer, and I don’t think lawyers are in the habit of saying “this is legal” without stipulating which laws and (potential) offenses we’re talking about.
I can tell you that if I were the commander who was given an order to invade Greenland (or anywhere), I would ask myself:
Can I authenticate that this order was issued by a Constitutionally appointed authority?
Does the order comply with my known lawful rules of engagement?
Does the order require me to break any other federal laws, to the best of my knowledge?
Does the order comply with the laws of warfare? (principally thinking about harm to non-combatant people and structures, or use of outlawed techniques of war).
If the action has been in progress more than 48 hours, has the President notified Congress per the War Powers act?
If the action has been in progress more than 90 days, has Congress authorized it via AUMF?
If all of the above are true, then I have no known grounds to challenge the order as being unlawful, therefore I have to follow it.
It’s also worth noting that it isn’t just political appointees who are subject to this calculation. Everyone from top to bottom is expected to be conscious of whether orders are lawful or not, and they’re given instruction (suitable to their role) to help them do so. A buck private is expected to know and follow the rules of warfare. They’re not expected to know the War Powers act, but if they do know an order violates it, they’re empowered (and in fact obligated) to refuse the order.
And this is where it gets tricky. Your “principally” is spot-on.
But one of the laws of war is “No invading for conquest or spite or fun.” That nebulous standard (that the US has admittedly not always followed scrupulously) will be the linchpin upon which the OP’s entire scenario turns.
And IMO a sober cautious President would get a much larger pass on this than would a volatile incautious President. And quite rightly so.
If we want to focus on illegalities, just to get back to the original point, let’s further stipulate that the president in this scenario orders the use of a nuclear weapon (let’s say of a small island off the coast of Greenland to intimidate the Greenlanders into submission.) That’s a violation of various treaties the U.S. has signed.
They can refuse to comply with that order, right? Because it’s a violation of a treaty? Or is a treaty not a law?
Treaties are binding agreements between nations and become part of international law. Treaties to which the United States is a party also have the force of federal legislation, forming part of what the Constitution calls ‘‘the supreme Law of the Land.’’
Under the Treaty Clause of the Constitution, the President has sole authority to enter into treaties. The Senate is to advise and consent on such treaties, and if they do so by a 2/3rd majority, then that treaty becomes law (not as a US code, but in the same sense that SCOTUS decisions are law). So it’s possible that for a treaty not ratified by Congress, the President could simply say “that treaty is canceled, bombs away”.
Greenland was probably not a good example for me to pick, because it’s part of Denmark, which is a NATO member, which makes it very thoroughly protected by Senate-ratified treaties.
A better example might be Venezuela. I can’t think of any active treaties the US has with them. So if the President decided to start nuking military targets in Venezuela, just on the general pretext that they’re a hostile government and we’re tired of their shit, I can’t think of any legally defensible basis to refuse that order. As long as the targets are demonstrably military in nature.
Though, hilariously, if he nuked Venezuela and did not kill any belligerents or destroy any property, then that would be colorable as a nuclear test, and it would violate the Comprehensive Nuclear Test Ban treaty, which was ratified by the Senate, and therefore such a strike would be illegal under US law. So if you’re going to nuke a country, you have to make sure you kill some people (belligerents). That’s not a super rigorous analysis though, so don’t hold me to that. When we’re talking about that kind of power, the only real law is might makes right.
If we want to keep our democracy, it never will. Otherwise, we will become like Rome where the general with the strongest legion held the most political sway.
I would imagine that any enemy soldiers (i.e., a few Venezuelan troops stationed on an island off the coast) would qualify as belligerents. They’re armed forces of a government hostile to U.S. interests.
In some respects, they’re belligerents if POTUS declares them to be so. And for darn sure they’ll be belligerent after they’ve been attacked. At least the survivors will. Hopping mad in fact. So there’s that.
