This is measured via election participation, so a confounding factor is the recent uptick in voter suppression tactics; these tactics are employed most visibly in states with large minority populations (e.g. states in the Deep South).

These tactics include: consolidating polling places in urban areas; restricting the ability to submit an absentee ballot or otherwise vote by mail; restricting early voting; voter ID laws; and "poll watchers" who intimidate those at polling places, sometimes illegally.

Moreover, those forced to vote in-person at polling places are not given time off from employment to do so. This overwhelmingly disenfranchises the working class, who just so happen to overwhelmingly vote for progressive policies that favor the working class over the middle/upper classes.