Each State contracted their responsibility for defense against invasion to the US government; the US government has breached its contractual duties and failed to protect the States against invasion.
What do you do with an employee like that? Fire them, and get the job done however you see fit. Then, when the derelict contractor complains, what do you tell them?
Article I, Section. 10.
Clause 3: 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.
Article IV, Section. 4.
The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.