If the constitution still mattered, Article I, Section 10 would prohibit this:
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.
It would be allowed if Congress consents. If they ever get to that point, watch out.