then it was "exempt" from statehood. However the statehood argument has been that there be a "designated" area within the District to be considered "the (federal) District/seat of the U.S. (to include the Capitol, it's office buildings, the White House, Supreme Court, etc.) " and the rest (municipal/residential) be considered the "state".
I.e.,
Why Statehood for DC
(snip)
Statehood for Washington, DC is constitutional:
The Constitution sets only a maximum size, “ten miles square,” for the federal district that is the “Seat of the Government of the United States.” Congress has the authority to redefine the borders of the federal district and shrink its size, as it did in 1846, when the portion west of the Potomac was returned to Virginia (now Arlington and Alexandria Counties.
Creating the new state will require a simple reduction in the size of the federal district to an unpopulated area which includes the US Capitol, the National Mall, museums, some federal office buildings, the White House, the Supreme Court, and major national monuments.
https://statehood.dc.gov/page/why-statehood-dc
ETA - U.S. Constitution
Article I
(snip)
Section 8.
The Congress shall have power to--
(snip)
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 the 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;
https://www.law.cornell.edu/constitution/articlei
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