The Los Angeles district attorney, Jackie Lacey, is a Democrat who has benefited from the public’s perception that she is a reformer. This is something she has fed herself, bragging to a Los Angeles Sentinel reporter that she has read “The New Jim Crow” by Michelle Alexander and has seen Ava DuVernay’s documentary “13,” about the connection between slavery and mass incarceration. But Ms. Lacey’s values have consistently lagged behind those of her constituency.

In ballot initiatives, Los Angeles County residents supported shorter sentences for low-level and nonviolent property and drug crimes and wanted to legalize recreational marijuana use for adults. Ms. Lacey opposed both. And although the county voted in favor of abolishing the death penalty, she continues to support it. Last year there were just 31 death sentences nationwide. Ms. Lacey’s office secured four of them.

Philadelphia’s former district attorney R. Seth Williams was once identified as a rising political star. But it turns out he wasn’t much of a leader at all. By the end of his tenure, which was cut short after he pleaded guilty to bribery and resigned, Philadelphia had locked up more of its residents per capita than any other major city. One in four defendants was being held in jail simply because of an inability to pay bail.

Mr. Williams had also won praise for agreeing not to pursue life-without-parole sentences again for 300 juvenile offenders. The Supreme Court has ruled they were unconstitutionally sentenced to such punishments and entitled to new sentencing hearings. But less than a year later, he reneged on his promise and denied ever making it.

America incarcerates more people than any other country, and it is prosecutors who are largely responsible.

So it’s especially frustrating that many of those who are praised as change-makers are at best making bite-size improvements. And because they say the right things, the public gives them a pass: Mr. Vance is running unopposed for a third term, and Ms. Lacey also ran unopposed in her last election.

The progressive bombast is meaningless if prosecutors continue to promote the same harsh practices behind the scenes. Instead, voters must look closely at their policies and hold them to high and specific standards. We should ask: Are prosecutors opposing new mandatory minimum sentences during legislative debates? Have they declined to request cash bail in a vast majority of cases? Are they keeping children out of adult court and refusing to seek life-without-parole sentences for them?

Over 1,000 prosecutors will be up for election next year in places like Dallas, San Diego, Seattle, Oakland, Calif., and Charlotte, N.C. Voters ought to make sure the people who win these crucial races are actual criminal justice reformers, not just people who say they are.