This is purely hypothetical the fact pattern.

Nation U is a member of the “N” defense treaty organization.  Nation T is also a member.

The N Treaty requires that all  N Treaty members defend the other members if they are attacked, if the attacked member requests.

U is at war with D that has engaged in military acts on U’s territory sufficient to trigger a duty to respond by the N Treaty member states.

The U Constitution requires that the U Senate approve all Treaties. It does not address abrogation of treaties. It vest the power to interpret treaties in U’s judicial branch.

The U constitution gives the U Congress the power to declare war but also provides that a governor of a single U state may use the state’s own military to defend the country from an aggressor if threatened with an imminent attack. The power of the President to act to defend U in case of an attack does not require a declaration of war.  An order from the U President can authorize nuclear war destroying planet E in less than 20 minutes without any consultation with U Congress or U Judicial branch.

U has conclusive proof that T has joined D as a enemy state. Does the U President have to abrogate the N treaty to defend against a direct attack by T?

What if the U President learns of conclusive proof of an imminent attack by D that will be assisted by T?

Is the N treaty abrogated related to the non-T members if U attacks T?

Does the U Constitution require that the U President obtain a court order before attacking T?  Can a court order abrogate defense obligations to one N treaty member while leaving unchanged the treaty obligations to other member states?

What result and why.