Insofar as elected officials are responsive to the policy views of their constituents, only the views of affluent and middle-class people really matter. The preferences of millions of low-income citizens (in the bottom third of the income distribution) have no discernible effect on senators' roll call votes, whether we consider the whole range of issues that come before Congress or specific salient roll call votes focusing on the federal budget, the minimum wage, civil rights, and abortion. Aristotle wrote that "where the possession of political power is due to the possession of economic power or wealth ... that is oligarchy, and when the unpropertied class have power, that is democracy." By that standard, America is, at best, a very unequal democracy.
I'm not sure how you can read Aristotle's definition and look at American politics today and not conclude that we have are essentially an oligarchy. If you are not at least of the middle class you have no real voice in the public arena. Even those who are comfortably middle-class are not as influential or connected to the process as those the wealthiest. When you have one political party whose entire purpose is to serve their corporate masters and wealthy base and another party that ignores the working class and is only slightly less amendable to the demands of corporate America then the existence of a functioning democracy is seriously in question.