Did the feds pay for this land as required by the Constitution’s Clause 17 of Section 8 of Article I and / or the eminent domain provision of the 5th Amendment?
And if this land was purchased from a state, did the state legislature consent to the deal as required by Clause 17?
Good constitutionally-based questions.
My argument (like yours, I think) with another on this thread is, if it’s not delegated to the feds by the Constitution, it belongs to the states or the people of the states. Since Art IV,Sec 3,Cl 2, gives the feds power over territories, then it would seem to me the feds have power to negotiate the terms of the agreement to transfer a territory into a state, but not for unconstitutional purposes or powers not delegated. Beyond the initial agreement and transaction, I believe the feds have no right to retain lands within a state unless for specific constitutionally-allowed purposes.