In 2015, there are few more effective instigators of national conversation than HBO’s John Oliver. The comedian recently devoted an entire half-episode of his program, Last Week Tonight, to the subject of mandatory minimum prison sentences, calling them a “mistake.” They do “way more harm than good,” he added.

It was the latest example of the increased scrutiny given to mandatory minimums, which were widely adopted during the 1980s and ’90s. Amid an emerging bipartisan consensus that America has incarcerated too many people for too long, President Obama this year backed the Smarter Sentencing Act — sponsored by Republican Senator Mike Lee and Democrat Senator Dick Durbin — which would cut many mandatory minimums for federal crimes in half.

Most mandatory sentences apply to drug offenses, but state and federal lawmakers have enacted them for gun crimes. They were on the agenda again this week when the Major Cities Chiefs Association convened the nation’s top urban police bosses in Washington, D.C., to discuss a spike in big-city violent crime after decades of decline. Chicago Police Superintendent Garry McCarthy, speaking to a reporter at the conference, made it clear he believed harsher judicial sentences for gun crime are necessary to stem the tide.

With mandatory minimums a hot-button issue across the political spectrum, it’s worth asking why courts impose these penalties in the first place, and what they’re supposed to accomplish.

Who came up with mandatory minimums?

In the United States, mandatory minimum sentences for criminal convictions have been around since the 18th century, when Congress declared a slate of federal crimes automatically punishable by death. It was not until 1951, when Congress passed the Narcotic Drug Import and Export Act, that America saw mandatory minimum sentences applied to crimes related to social problems, mainly drugs. A handful of states subsequently enacted their own mandatory minimums for drug convictions, the most well-known of which are New York’s decidedly harsh 1973 Rockefeller drug laws.

Gun crimes weren’t covered by federal mandatory minimums until the Reagan-era Armed Career Criminal Act passed in 1984. The sentences usually apply to gun crimes committed in the course of another crime, especially drug trafficking or a violent offense. Possessing a gun while selling drugs can add anywhere from five to 30 years to a felon’s sentence, depending on prior convictions and the type of weapon. According to a 2011 report prepared for Congress by the United States Sentencing Commission, mandatory minimums for gun crimes are the penalty most commonly added to an original charge.

Far less common are mandatory minimums solely for illegal possession of a gun. The Armed Career Criminal Act applied strict 15-year penalties for those caught in possession of a gun after being convicted three times or more of certain drug or violent crimes, but the Supreme Court has invalidated portions of those criteria as being too vague.

Do some states have their own mandatory minimums for gun crimes?

Yes. In 1974, Massachusetts rolled out a one-year minimum sentence for carrying a handgun without a license. New York City Mayor Ed Koch championed a 1980 state law imposing a one-year sentence on those convicted of possessing a loaded, illegal gun on the street, though he made many concessions to get it passed. In 2006, New York raised that penalty from one year to three-and-a-half years, regardless of previous criminal history. This law was accompanied by a New York City public relations campaign that blanketed the city with ads that read, simply, “GUNS = PRISON.” (The effort was lead by then-Mayor Michael Bloomberg, founder of Everytown for Gun Safety, a seed donor to The Trace.)

Most other jurisdictions only impose mandatory minimum sentences for illegal firearm possession when the accused is already a felon. Minnesota sentences felons possessing a gun to a minimum of five years, though like most mandatory minimums (including New York’s), the law contains so-called “safety valves” that create exceptions to those offenders deemed lower threats. Wisconsin’s Assembly recently sent a bill to the State Senate that would mandate prison terms of three years for violent felons in possession of a gun. Michigan and Florida already have such laws. Federal charges for the same crime do not carry mandatory minimums, but rather statutory maximums of 10 years in prison.

Several states have considered similar measures but have failed to enact them. Chicago Mayor Rahm Emanuel embarked on a high-profile campaign in 2013 to get Illinois to adopt mandatory minimums in line with New York’s law. The bill died in the legislature.

There are no mandatory minimums anywhere for illegal gun trafficking. Penalties for that crime vary widely.

What are the arguments in favor of these sentences?

Proponents argue that they deter future gun crime: Knowledge of the stiff penalties, the argument goes, makes people think twice before illegally acquiring a firearm. And when an offender is convicted under mandatory minimums, the laws ensure that he or she will remain locked up for an extended period, unable to commit further crimes during that time.

Mandatory minimums are also supposed to make punishments not just stronger but more consistent — and theoretically more fair — by corralling sentencing authority. Without such measures, it’s easier for judges to dole out unduly harsh sentences based on biases, or give slaps on the wrists that fail to recognize the risks some defendants pose if quickly returned to their neighborhoods. With the mandates, everyone convicted of a given offense should face the same punishment. Policymakers frustrated by gun violence see mandatory minimums as an imperfect recourse when the judicial system, left to its own devices, is not getting dangerous people off the streets.

Finally, there’s the clear moral statement that mandatory minimums send about which crimes society considers most serious. The Heritage Foundation has argued in defense of the laws on these grounds, since they’re imposed by elected legislators and thus reflect the public’s values.

For proof of the laws’ effectiveness, supporters point to the dramatic nationwide fall in crime during the 1990s, which followed a push for mandatory minimums for drug and gun crimes.

What are the arguments against them?

First, that the mandatory minimum regime for drug crimes in place since President Reagan has been unduly harsh, and that even for gun crime, the primary effect of mandatory minimums has not been a safer society but an exploding prison population. While consigning offenders to financial hardship, the laws, in this view, also cost society enormous amounts of money.

Additionally, given prosecutors’ latitude in bringing cases, the laws don’t necessarily make good on their promise of fairness and consistency. Sentencing standards only matter when there’s a successful conviction, which requires a charge in the first place. If a prosecutor opts not to charge certain categories of people with crimes that carry mandatory minimums, or does away with charges during plea bargaining, it may not matter if the judge is required to issue consistent sentences.

Criminologist Michael Tonry at the University of Minnesota also argues that sentencing itself is generally a poor way of deterring many kinds of crime, since “certainty and promptness of punishment are more important than severity.”

Are mandatory minimums effective?

The evidence that they directly reduce crime is thin, according to a review by Northwestern University School of Law. Even in the case of New York City, which had one of the country’s most dramatic reductions in gun crime, some experts question how much greater public safety can be clearly attributed to these laws. University of California at Berkeley professor Michael Zimring studied the city’s historic crime decline from the ’90s into the 2000s, and found that 90 percent of the reduction in murders happened before mandatory minimums for gun possession were tightened up in 2006.

In 2013, President Obama issued an executive order to the Center for Disease Control to produce a study on the best means of reducing gun violence. The study was generally short on hard conclusions, but on the subject of mandatory minimums, it found the efforts of prosecutors and judges less effective at reducing gun violence than community programs and on-the-ground policing. “Most studies found that enhanced sentencing did not affect crime rates,” the report read.

[Photo: Flickr user Surrey County Council News]