The District of Columbia Voting Rights Amendment was a proposed addition to the Constitution which would have granted Washington D.C. more power in elections. It basically would grant them more votes in the electoral college, and seats in both the House and the Senate. It was approved by Congress in the late 70's, but few states ratified it by the time of it's expiration in 1985.
I honestly think it's good that it didn't pass. I feel sympathy for the voters of D.C. but I think it's more than fair if it was counted as part of Virgina or Maryland in national elections than it to have a considerable amount of power for such a small population.