The sandwich is named for the sauce, and the sauce is the only thing about it that is specific to Washington: mumbo sauce, a sweet, tangy, red condiment that sits somewhere between barbecue sauce and a sweet-and-sour glaze and exists, in this exact form, almost nowhere outside D.C. carryout counters. Fried chicken wings go on plain white bread, get doused in mumbo, and that is the sandwich. The wings are the substance but the sauce is the identity. Without mumbo this is just fried chicken on bread; with it, it is a piece of one city's carryout culture, where mumbo goes on wings, fried rice, and fries with equal authority.
It works because the bread is doing a job no one talks about: it is a sponge, not a structure. White sandwich bread is chosen precisely because it soaks up the loose, sticky mumbo and the fry grease and turns into the part of the sandwich that delivers the sauce, while giving the hand something to hold bone-in wings with. The wings are fried hard so the skin stays crisp under the sauce for the first few bites, and the sauce is applied heavy and late so it coats rather than marinates. There is no garnish and no acid counter beyond the tang already built into the mumbo, which is the honest design of carryout food: hot, sweet, sticky, fast, eaten from the bread it was wrapped in. The bones stay in, which tells you this is a sandwich in the loose carryout sense, assembled to be cheap and immediate rather than tidy.
The variations are mostly about the protein under the sauce. Boned wings keep the bread-as-sponge logic intact. Fried chicken tenders or a fillet swap in for a cleaner, one-handed version. Each of those deserves its own article rather than being crowded in here.