Article I, Section 10:
“No State shall, without the Consent of the Congress...enter into any Agreement or Compact with another State...”
NPV has another obstacle to overcome.
Article II, Sec 1
“No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States.”
They have already gutted the Constitution by just ignoring what is inconvenient.