On May 8, President Donald Trump announced US withdrawal from the Joint Comprehensive Plan of Action, colloquially known as "the Iran nuclear deal."
While that decision has come under criticism for being both a really bad idea and a severe betrayal of trust, both of which are true, it's worth noting that the US withdrawal is also a breach of treaty obligations, and that such obligations are, per the US Constitution and co-equal with it, "the Supreme Law of the Land."
But wait -- aren't defenders of the withdrawal correct in noting that the JCPOA isn't a treaty at all? Yes, they are, although some err in referring to it as an "executive order." It isn't even that. It's merely a "State Department Political Commitment" which can be wadded up and thrown in the trash any time ...
... except that the treaty in question is not the Joint Comprehensive Plan of Action. It's the United Nations Charter, delivered to the US Senate by President Harry Truman and duly ratified by that body on July 28, 1945 by a vote of 89-2.
Under Article 25 of the UN Charter, "members of the United Nations agree to accept and carry out the decisions of the Security Council."
On July 20, 2015, the members of that body, including the United States, unanimously endorsed the Joint Comprehensive Plan of Action in UN Security Council Resolution 2231.
It seems unlikely that Samantha Power, US ambassador to the UN at the time, didn't know what she was committing the US government to when she voted for the resolution rather than exercising the US's veto power on the Security Council. After all, the resolution itself contains text "[u]nderscoring that Member States are obligated under Article 25 of the Charter of the United Nations to accept and carry out the Security Council's decisions."
Was the JCPOA a "good deal?" Not especially so for the Iranians. Even though they apparently had no nuclear weapons program after 2004 at the latest, and even though they were apparently in full compliance with their obligations under the Non-Proliferation Treaty (unlike the US), they made a bunch of concessions to US demagoguery (and demagoguery from Israel, an ACTUAL rogue nuclear state) in order to get some of their own money (seized by the US government) back and get some sanctions (which should never have existed) lifted.
For the US government, it was an excellent deal, a face-saving way of hitting the reset button on nearly 40 years of failed policy vis a vis Iran. By letting Iran rejoin "the civilized world," the US received the same opportunity -- an opportunity that Trump just blew by way of loudly warning the world that the US government can't be trusted to keep its word. Or honor its treaty obligations.