You might be thinking of the Princeton study which determined that policy is mainly influenced by wealthy interest groups[1]. The conclusions rang true with how a lot of people see the system operate in the past century. Interestingly enough, this was ranking higher in search results, when I was looking for a link to the study itself[2]: "Remember that study saying America is an oligarchy? 3 rebuttals say it's wrong." Worth noting that the VOX article finds high agreement between the rich and middle class, while the lower class appears to get their policies enacted in less than one fifth of the cases.

[1]: https://scholar.princeton.edu/sites/default/files/mgilens/fi...

[2]: https://www.vox.com/2016/5/9/11502464/gilens-page-oligarchy-...