Article 1, Section 8, Clause 17

"To exercise exclusive legislation in all cases, whatsoever, over such district (not exceeding ten miles square) as may, by cession of particular states, and the acceptance of Congress, become the seat of government of the United States, and to exercise like authority over all places purchased by the consent of the legislature of the state in which the same shall be, for the erection of forts, magazines, arsenals, dockyards and other needful buildings;.."

In addition to its limited and specifically enumerated powers, Congress maintains under this provision "exclusive legislative jurisdiction"as regards isolated "federal enclaves" established for the specified purposes within State territorial boundaries with consent of the State legislature. These specified areas are not subject to the Constitutional system of dual sovereignty that is maintained under the "federal" system with the States, but are governed directly by Congress, "exclusive" of State legislative jurisdiction. Their government is purely a creature of the legislature, not originating from the process of social compact and convention. Although federal enclaves, such as military facilities, are sites located within State boundaries, they are areas considered "foreign" - external to the States.  Congressional legislative jurisdiction as pertains to these areas includes the full scope of "police powers" that are otherwise reserved to the States. (See Understanding American Property Rights, Part III.)

In Pollard v. Hagan, 44 U.S. 212 (1845) Justice McKinley clarified that although the exclusive legislative jurisdiction of Congress extended over the territories, this plenary power did not survive statehood. Although it retained ownership title, Congress had no power under Article I, Section 8, Clause [currently] 17 to exert exclusive legislative jurisdiction over the "public lands" retained in ceded ownership by the United States:

"When Alabama was admitted into the union, on an equal footing with the original states, she succeeded to all the rights of sovereignty, jurisdiction, and eminent domain which Georgia possessed at the date of the cession, except so far as this right was diminished by the public lands remaining in the possession and under the control of the United States, for the temporary purposes provided for in the deed of cession and the legislative acts connected with it. Nothing remained to the United States, according to the terms of the agreement, but the public lands. And, if an express stipulation had been inserted in the agreement, granting the municipal right of sovereignty and eminent domain to the United States, such stipulation would have been void and inoperative: because the United States have no constitutional capacity to exercise municipal jurisdiction, sovereignty, or eminent domain, within the limits of a state or elsewhere, except in the cases in which it is expressly granted.

"By the 16th clause of the 8th section of the 1st article of the Constitution, power is given to Congress 'to exercise exclusive legislation in all cases whatsoever, over such district (not exceeding ten miles square) as may by cession of particular states, and the acceptance of Congress, become the seat of government of the United States, and to exercise like authority over all places purchased, by the consent of the legislature of the state in which the same may be, for the erection of forts, magazines, arsenals, dock-yards, and other needful buildings.' Within the District of Columbia, and the other places purchased and used for the purposes above mentioned, the national and municipal powers of government, of every description, are united in the government of the union. And these are the only cases, within the United States, in which all the powers of government are united in a single government, except in the cases already mentioned of the temporary territorial governments, and there a local government exists. The right of Alabama and every other new state to exercise all the powers of government, which belong to and may be exercised by the original states of the union, must be admitted, and remain unquestioned, except so far as they are, temporarily, deprived of control over the public lands."

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