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p.p.s. Claims - see comments - that the war was already illegal according to US laws and that a ratified treaty wouldn't change anything are just that hogwash. Yes, Congress is supposed to authorize war, but this "isn't a war". We almost never have any wars left on the planet these days and POTUS is in charge of foreign policy (treaty ratifications and war declarations aside). And in practice, for the last 80 yrs or so POTUS has largely "done their thing" by running undeclared wars under a "I am in charge of foreign policy" claim of authority. That's what War Powers Act of 1973 was supposed to fix, after Vietnam saw a even more massive "non-war". Didn't really happen, and there have been questionable cases since, even though this war dwarfs them all in magnitude. Whether this type of military adventure is legally, per US domestic law, within the rights of the President to decide or not is for SCOTUS to decide. However, not abiding by a ratified treaty would clearly be an abuse of presidential power.

p.p.s. Claims - see comments - that the war was already illegal according to US laws and that a ratified treaty wouldn't change anything are hogwash. Yes, Congress is supposed to authorize war, but this "isn't a war". We almost never have any wars left on the planet these days and POTUS is in charge of most foreign policy (treaty ratifications and war declarations aside). And in practice, for the last 80 yrs or so POTUS has largely "done their thing" by running undeclared wars under a "I am in charge of foreign policy" claim of authority. That's what War Powers Act of 1973 was supposed to fix, after Vietnam saw a even more massive "non-war". Didn't really happen, and there have been questionable cases since, even though this war dwarfs them all in magnitude. Whether this type of military adventure is legally, per US domestic law, within the rights of the President to decide or not is for SCOTUS to decide. However, not abiding by a ratified treaty would clearly be an abuse of presidential power.

p.p.s. Claims - see comments - that the war was already illegal according to US laws and that a ratified treaty wouldn't change anything are just that hogwash. Yes, Congress is supposed to authorize war, but this "isn't a war". We almost never have any wars left on the planet these days and POTUS is in charge of foreign policy (treaty ratifications and war declarations aside). And in practice, for the last 80 yrs or so POTUS has largely "done their thing" by running undeclared wars under a "I am in charge of foreign policy" claim of authority. That's what War Powers Act of 1973 was supposed to fix, after Vietnam saw a even more massive "non-war". Didn't really happen, and there have been questionable cases since, even though this war dwarfs them all in magnitude. Whether this type of military adventure is legally, per US domestic law, within the rights of the President to decide or not is for SCOTUS to decide. However, not abiding by a ratified treaty would clearly be an abuse of presidential power.

p.s. As noted in a comment under the question, I am waiting to see what was really agreed to and I am rather skeptical that it is Iran's laundry list cited above. We know there is a 2 week ceasefire, during which negotiations are meant to take place and I would expect the final shape of the terms to become clear then, not now. Without that agreement what we have right now are Iranian demands and a temporary ceasefire with somewhat uncertain rules. Along with a US administration desperate to spin it into a "win". No more, no less.

And how would that be "enforced" upon the US? As per this other answer, pretty much by Iran keeping the same cards as they currently have: the capacity for mayhem in the region. Ditto for a POTUS-only agreement.

p.s. As noted in a comment under the question, I am waiting to see what was really agreed to and I am rather skeptical that it is Iran's laundry list cited above. We know there is a 2 week ceasefire, during which negotiations are meant to take place and I would expect the final shape of the terms to become clear then, not now. Without that agreement what we have right now are Iranian demands and a temporary ceasefire with somewhat uncertain rules. Along with a US administration desperate to spin it into a "win". No more, no less.