The entirety of US "democracy" has been oligarchical. Voting was originally restricted to white landowning men and naturally the only people who could "serve" as representatives were the richest people from that group. Everyone has always had to struggle to get anything at all and even then it would be incomplete or weak - like getting the right to vote for your oppressor. The largest liberatory changes required violence and direct action, with the most dramatic being the ability of slavery and the battles of the labor movement. And at no point has the root of oppression (and the oligarchy) been overturned: capitalism.