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It may take a constitutional amendment but at least the part of making DC's representatives having voting rights in the House like those of any other district should have gathered a big consensus. It puzzles me why not, maybe it's a too red or too blue of a district, I don't know.
As to raising DC to a state-equivalent for senatorial representation purposes I don't think its size is that big of a deal because at least Wyoming is less populated than DC. That's the Brazilian (and others) solution. There are other solutions like pooling all diverse non-states in one big senatorial electoral area or just pooling the Pacific territories with Hawaii's electoral area, DC with Virginia or Maryland's area and creating a new one that pools PR with the USVI...
All this if one wants to preserve a symbolic federal capital like Falecius suggested but if more like you don't think of it as a big deal... then there you go...
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There wouldn't be a consensus on giving DC representation in the House. In any case handing the city over to Maryland or Virginia would be MUCH easier and quicker. Give one the capital and the other a couple of billion dollars in compensation.