But D.C. it seems has a particular problem associated with its statehood, centering around two constitutional clauses: Article I, Section 8, clause 17 and the Twenty-Third Amendment.
The first is the one that enabled the establishment of D.C. in the first place: it gives Congress the power 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."
The second gives that territory -- "[t]he District constituting the seat of Government of the United States" -- electoral votes "equal to the whole number of Senators and Representatives in Congress to which the District would be entitled if it were a State", provided that it cannot be more than the least populous state (which is to say, it can't be more than Wyoming's three). That last proviso has been moot since the Amendment's adoption, since D.C. would only be entitled to three electoral votes anyway.
These two clauses together pose a problem.
Because Article I, Section 8, clause 17 gives Congress superior power to exercise legislation over the "District" which is the "Seat of Government", one could not form a state -- or at least, a state whose statehood is equal to that of California or Arizona -- in that "District". An important part of making D.C. a state is precisely that it gets the same authority to govern its own affairs just like any other state (no more Mayor Franks!). And of course, if the state of D.C. does grow populous enough, then it should be able to gain its rightful proportion of electoral votes.
So D.C., the state, has to be a separate entity from the constitutionally-described "Seat of Government" "District". On it's own, that's easily surmountable: Congress shrinks this "District" (whose area only has a maximum, not a minimum) to the barest possible limits -- probably the White House, Capitol, Supreme Court, and National Mall -- and then grants statehood to the remainder (another possibility is to retrocede the territory back to Maryland -- but the below problem still applies)
But the problem is that in that world, the 23rd Amendment remains in play, and that rump "District" -- which (hopefully) has no people in it -- still is entitled to the amount of electoral votes it would be entitled to were it a state.
How many electoral votes is that, and how do they get appointed? Well, that depends on how many "Senators and Representatives in Congress to which the District would be entitled if it were a State". One answer is zero: since nobody lives there, it would get no congressional representation at all. But that doesn't actually track the constitutional text: Article I, Section 3, clause 1 gives each state two Senators, period, without respect to population. And while Article I, Section 2, clause 3 does apportion congressional representatives be population, it also guarantees that every "state" shall receive at least one representative.
So now we have a problem: even after D.C. statehood, there still will likely be a rump "Seat of Government" that has no people but three electoral votes. What to do? I see two possible solutions:
- Have no "Seat of Government". The Constitution permits the establishment of this Seat of Government, but it doesn't require it. Moreover, the same provision which permits Congress to establish a seat of government also allows it to exercise authority over places "purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings." So Congress could "purchase" the White House from D.C. for a nominal fee, at which point it is a federal building (like a fort) but still in the state of D.C. (rather than the Seat of Government).
- Allocate the "Seat of Government's" electoral votes to the national popular vote winner. The Twenty-Third Amendment guarantees the Seat of Government three electoral votes, but it also specifies that these electoral votes shall be appointed "in such manner as the Congress may direct". So Congress could "direct" that they appointed really any way it likes, but the most natural choice is to whichever candidate receives the most votes nationwide. This would have the additional salutary effect of -- in a very slight way -- giving meaning to the national majority in Presidential elections, which (as 2000 and 2016 have painfully shown) currently has no weight whatsoever.