The U.S. Constitution, under Article I; Section 9 - Limits on Congress; 6th clause stipulates that: "No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law; and a regular Statement and Account of the Receipts and Expenditures of all public Money shall be published from time to time."
However, undisclosed amounts of unaccounted for public Money are being withdrawn to pay for the salaries, and support of the U.S. Agents sitting on the Security Council Resolution 2231 created Joint Commission, and Procurement Working Group bureaucracies. These two bureaus are responsible for overseeing ongoing expediting of Iranian acquisitions of nuclear weapons associated assets; while preventing the IAEA from inspecting any aspect of these U.S. expedited, Iranian acquisitions.
Aside from the problem that the financial support for U.S. representation on this Iran weapons acquisition project is completely unaccounted for; there is absolutely no domestic law which supports it. Resolution 2231 was never submitted to Congress by President Obama, and the Congress never voted on it. Congress only voted on the JCPOA part – and didn't come close to approving that. So there is no justification for the funding and withdrawal of Moneys from the Treasury for this project must be reasonably understood as anti-Constitutional.
No problem there; Congress has a solution; it simply doesn't talk about Procurement Working Group ongoing activities. From the summer of 2015 through October 2017 the Congress never mentioned a word about the Procurement Working Group. In Oct. 2017 Congress let it slip out that it had known about the project the whole time. The pretense notwithstanding, Congress has a duty to know, and to tell.
In late Oct. 2017, some Republican Senators finally were surprised that the IAEA is prohibited from checking on Iranian work with multi-point detonation systems suitable for creating a nuclear implosion warhead. This work has been allowed by Resolution 2231 since 16 January 2016.
Perhaps Congresspersons of the 114th and 115th should have read the resolution more carefully before they simply decided to ignore it.
In January 2018, Republican Senator Inohofe squawked on the floor of the Senate that North Korea had suddenly shown plausible capacity to hit anywhere on the continental U.S.; and yes, there is evidence.
Perhaps 115th Congresspersons might have taken a common sense interest into look into the matter of what the U.S. Government is assisting North Korea's best trading buddy, Iran, is acquiring through U.S. sponsorship. If the Congress had shown some responsibility, and interest; then the Congress have expected the sudden leaps of North Korean ballistic missile capacity.
President Trump himself presented a solution to this pandemonium. In mid-January 2018, he declared that he would continue to maintain the status quo for 120 days. Almost as an excuse for his apparent confusion on the issue; he proposed several preposterous conditions which, if accepted Congress; he suggested that he might agree to continue supporting the situation indefinitely; regardless that there is no legal funding mechanism in place to support the resolution; which, in its design to promote the proliferation of nuclear weapons capacity, violates at least the Charter of the United Nations, the Treaty on the Non-Proliferation of Nuclear Weapons (Nuclear non-Proliferation Treaty, NPT), and peremptory norm of general international law.
Don Trump has no domestic or international legal footing to continue supporting Resolution 2231. He can, however, put a stop to this entire menace by bringing this international malfeasance to the International Court of Justice to have the whole resolution thrown out.
Parties would be forced to bring their relations back in line with international norms, The Court could order how that must be done. But Donald Trump doesn't seem to give what can be accomplished through the law much thought.