American voters have realized that prosecutors hold the keys to a fairer criminal justice system. In November’s elections, they replaced numerous incumbents with reformers who promised to reduce mass incarceration, its exorbitant costs and its racial disparities. Prosecutors are central to solving these problems because they control two of the most important decisions in the criminal process: who will be charged with a crime and what that criminal charge will be.

But in practice they do not decide alone. In the enormous world of misdemeanor processing, the police quietly wield a lot of prosecutorial authority. So for voters seeking change, switching prosecutors is only a partial solution.

In hundreds of misdemeanor courts in at least 14 states, police officers can file criminal charges and handle court cases, acting as prosecutor as well as witness and negotiator. People must defend themselves against, or work out plea deals with, the same police officers who arrested them for low-level offenses like shoplifting or trespassing.

Consider South Carolina, where most of the 400 magistrate and municipal courts had no prosecuting attorneys, according to a 2017 study by the National Association of Criminal Defense Lawyers. The police prosecuted their own misdemeanor arrests, while 90 percent of defendants had no lawyers and so faced the arresting officer-prosecutor on their own. South Carolina also does not require its lower-court judges to be lawyers, so thousands of convictions occur without input from a single attorney.