Demonstrators gather near the site where 18-year-old Michael Brown was shot and killed on Nov. 22, 2014, in Ferguson, Mo. (Eric Thayer/The Washington Post)

Tomorrow is an important day in American democracy. Yes, Chicago Mayor  Rahm Emanuel will find out if voters want him for a second term in what the New York Times called a “test case of liberalism.” But the municipal elections in Ferguson, Mo., will be a test case of anger. Will voters there use their outrage over the killing of Michael Brown and the inequities it exposed to change their local government? History says no.

The Aug. 9 shooting of Brown by then-Ferguson police officer Darren Wilson exposed troubling truths to the community and to the nation. In two harrowing Justice Department reports we learned that Wilson was justified in shooting Brown, but we also learned why the St. Louis suburb exploded the moment the unarmed African American teenager was killed. The majority-black town has a majority-white municipal government that financed itself through fees by criminalizing its citizens.

The statistics revealed by DOJ are enraging. African Americans are 67 percent of Ferguson’s population. Yet, the mayor (not up for reelection tomorrow) and five of the six members of the city council are white. The police force was 83 percent white. And collusion between the police department, municipal courts and city government, not to mention an overall air of racial bias, led to the trampling of the constitutional rights of Ferguson’s black majority cited in the DOJ report on the Ferguson police department.

Data collected by the Ferguson Police Department from 2012 to 2014 shows that African Americans account for 85% of vehicle stops, 90% of citations, and 93% of arrests made by FPD officers, despite comprising only 67% of Ferguson’s population….

FPD appears to bring certain offenses almost exclusively against African Americans. For example, from 2011 to 2013, African Americans accounted for 95% of Manner of Walking in Roadway charges, and 94% of all Failure to Comply charges….

Nearly 90% of documented force used by FPD officers was used against African Americans. In every canine bite incident for which racial information is available, the person bitten was African American…..

Municipal court practices likewise cause disproportionate harm to African Americans. African Americans are 68% less likely than others to have their cases dismissed by the court, and are more likely to have their cases last longer and result in more required court encounters. African Americans are at least 50% more likely to have their cases lead to an arrest warrant, and accounted for 92% of cases in which an arrest warrant was issued by the Ferguson Municipal Court in 2013. Available data show that, of those actually arrested by FPD only because of an outstanding municipal warrant, 96% are African American. …

[O]ur investigation has revealed that these disparities occur, at least in part, because of unlawful bias against and stereotypes about African Americans. We have found substantial evidence of racial bias among police and court staff in Ferguson. …

This evidence of bias and stereotyping, together with evidence that Ferguson has long recognized but failed to correct the consistent racial disparities caused by its police and court practices, demonstrates that the discriminatory effects of Ferguson’s conduct are driven at least in part by discriminatory intent in violation of the Fourteenth Amendment.

The statistics above highlight why Tuesday’s election is so important. Half of the city council is up for reelection. The six-member body that already has one African American member will gain at least one more. If change is to come to Ferguson, particularly its government, folks have to show up and vote. But there is an electoral history that Ferguson must overcome. As The Post’s Monkey Cage blog pointed out five days after the Brown shooting, even though blacks and white voted at comparable rates during presidential elections, 54 percent and 55 percent, respectively in 2012, only 6 percent of African Americans (and 17 percent of whites) showed up at the polls for municipal elections the following year.

The unconstitutional practices and the awful dynamic they created in Ferguson must change. And it’s going to take more than a scathing DOJ investigation to do it. The people who marched in the streets in the aftermath of the Brown killing now must march into voting booths to take direct control of their government. They have a chance to start to effect real change by electing a municipal council that not only better reflects the demographic makeup of its city but also its values. They must not blow this chance.

Follow Jonathan on Twitter: @Capehartj