You can not simply withdraw from a contract. If you could, there would be no need to have a contract, and no contract could protect a party when you pay money for a service. The party paid could then ‘simply withdraw’ from the contract.
Pretending to simply withdraw from a contract creates a controversy between the state and the federal government which would be, per the constitution, resolved with the Supreme court as original distribution.
Except in this case we have one party saying "I can change at-will any portion of this contract" which is exactly what the federal government has said in its actions. Consider the 4th, 6th, and 8th amendments and how the federal judicial system has impacted how they are applied. (Or even that despicable doctrine of incorporation; wherein the constitution's words magically change to constrain who the fed want; ex: States/counties/cities and the 1st Amendment.)
Consider also, the refusal of the federal government to abide by its contractual obligations (Art IV, Sec 4 & AZ).
What then is the proper answer?
You evidently need better reading skills. I did not say that you could simply withdraw from a contract unless the other party violated the terms and conditions of said contract. The federal government has broken its end of the bargain. The other parties are no longer bound to the contract.
The “contract” also does not explicitly forbid the states from leaving said contract. Since it is not expressly forbidden, that power is reserved to the states by the beloved 10th amendment. Which, for your reading pleasure, I will post now.....
“The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”
Since the right to secede is not prohibited, the states have the full right to do so.