The problem is this clause, not the Treaty clause:
No State shall, without the Consent of Congress, lay any duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.Unless the interstate compact is approved "with the Consent of Congress", the law is invalid, unconstitutional, or however you wish to describe it. The internet site mentions this fact, but hides it quite well. It is still a fact, however.
