The Democratic presidential candidates should look at what a growing number of prosecutors are doing to end mass incarceration.

The United States spends far too much money locking up far too many people for far too long.

A few years ago, a politician had to be brave to say anything like that out loud. Now it’s a mainstream and bipartisan view.

In a 2018 survey conducted for the American Civil Liberties Union, 59 percent of respondents said they would be more likely to support than oppose a candidate who supports reducing the prison population. Achieving that goal is now an accomplishment that politicians showcase. In December, Congress by wide margins passed the First Step Act to reduce some drug sentences and improve conditions in federal prisons. President Trump, despite painting a frightening picture of crime-ridden “American carnage” at his inauguration, invited the first drug offender released as a result to the State of the Union address.

It’s all pretty head-spinning after decades of elected officials competing to lock more people up and spotlight the scariest crimes. Now, with public opinion shifting far and fast and politicians hurrying to catch up, you could even argue that criminal justice reform has become the new marriage equality in terms of the turnaround in public attitudes.

That presents a major opportunity for Democratic presidential candidates. But for all the energy behind reform, no presidential candidate has articulated a big, comprehensive vision for transformational change. There’s a consensus that the system is broken, but no agreement on how to fix it.

The presidential candidate seeking to distinguish herself might start by looking at a new wave of reform-minded district attorneys who are challenging conventional law-and-order approaches in red states and blue ones.

For the candidates, thematically, a starting point should be that wealth should not determine a person’s fate in court, and profit should not drive the system. Bail bonds, privatized probation and corporate-run prisons are parasitic features of the justice system. Ending cash bail should be at the top of every candidate’s criminal justice agenda. So should getting rid of fines and fees that help fund local governments but trap people in cycles of debt.

Ferguson, Mo., became a symbol of the criminalization of poverty for routinely sending black defendants to jail for failing to pay minor traffic fines. But last November, a new district attorney, Wesley Bell, was elected. On his first day in office, he announced one of the most progressive bail policies in the country — pretrial release, without bail, for misdemeanors and some felonies, unless the prosecutor thinks there is a direct threat to public safety.

Mr. Bell also said his office would no longer seek to revoke probation for unpaid fines and fees. “As an overriding principle, I do not believe in prosecuting poverty,” he told a weekly newspaper, The St. Louis American.

The old Ferguson lives on elsewhere. In Texas, 524,000 people were jailed in 2018 for unpaid traffic tickets. Even short stays for nonviolent offenses can wreak havoc with people’s jobs and child care. Sparing them needless punishment matters for their lives.

To end mass incarceration, however, exempting nonviolent offenses from jail time isn’t enough. People convicted of violent crimes make up more than half of the country’s state prison population. But the image of prisons overflowing with murderers and rapists is wrong. In many states, “violent felonies” include offenses like breaking into an empty house or snatching a purse or iPhone on the street. Reducing sentences for these offenses — and changing what counts as a violent felony to begin with — can lower this share of the prison population.

And that fits in with a second theme for candidates: People deserve a second chance, because many grow and change. They robbed to feed an addiction and then got sober. They assaulted someone because they were mentally ill and then got treatment and stabilized. They mature as they age beyond their teens and early 20s. That’s why it makes sense to reconsider how long a person should stay in prison after doing some time.