A BROKEN TOOTH sent Antonio Amphy, an engaging 42-year-old with a grey goatee, behind bars for six months. After taking a pill to ease his pain, he failed a drugs test and broke the terms of his parole. (He is completing a 24-year sentence for a murder in 1994.) Mr Amphy has been sent back inside other times, he says, for smoking marijuana or failing to meet his parole officer.

Mr Amphy, who was released in Milwaukee last week, listens as others offer similar accounts. A woman says her depressed boyfriend was re-imprisoned for not meeting his officer—after attempting suicide he was in intensive care for liver failure. “He’s dying and they lock him up!”, she exclaims. A sex-offender on parole says his officer failed him over a lie-detector test. Six weeks back inside cost him his job and he came home to a trashed apartment.

Cases of technical revocations—dubbed “churn” or “back door entry to prison”—are dismally common. “Basically it’s impossible not to violate” parole conditions, suggests Pamela Oliver, a sociologist at the University of Wisconsin in Madison. Returning to prison undermines efforts to go straight. “This is going to continually mess up my life, it’s all so difficult trying to get started again”, says Mr Amphy, in tears. Revocations can reset the parole time remaining to be served. Though his sentence should be over, he still has five years to go.

That is both miserable for individuals and does little good for the state, because churn adds to an already over-stuffed prison population. In Milwaukee around one-third of those on parole go back inside at some point, says a local researcher. Reform campaigners say some 3,000 people in the state are reimprisoned each year despite committing no new crime, a rate they say is far above the national average.

Ed Wall, who until recently ran corrections in the state, calls this “an endless treadmill of throwing people back in prison for technical violations”. He wants to reform that. Carl Fields, another ex-prisoner, former “street dude, hustler and knucklehead” agrees. He served 16 years for shooting at (and missing) policemen when he was a teenager and will be on parole until 2033. An articulate campaigner, he also wants to close an overcrowded, high-rise, 1,000-bed prison tower, the Milwaukee Secure Detention Facility ( MSDF ). It appears to be a fortified office block downtown but is crammed with inmates on revocations.

Wisconsin has not taken lessons from other states that kept prison populations relatively low or have found ways to cut them. South Carolina and Michigan for example have adopted non-custodial means, such as community service, for those who break parole terms. South Carolina has cut its prison population by 12%, lowered spending and closed three prisons between 2010 and 2015.

Mr Fields says Wisconsin should “get on the same track” as Minnesota. The two states, roughly similar in population, size, wealth and culture, have adopted sharply different approaches to prison in the past 40 years. They form a natural experiment, contrasting Wisconsin’s tough-on-crime methods with neighbouring Minnesota’s more progressive ones.

The states diverged after the 1970s, when “liberals in Wisconsin saw ourselves as twinned with Minnesota”, says Kenneth Streit, a researcher in Wisconsin. Inmate populations (in prison and county-run jails) rose fast, partly because of hardening sentences in both states. Minnesota had locked away 132 inhabitants per 100,000 in 1978, which jumped to 434 people by 2015, says the Vera Institute of Justice. Wisconsin’s sentencing was tougher still: its inmate population leapt from 178 to 925 per 100,000 residents.

Wisconsin’s 35,000-strong jail and prison population now far exceeds Minnesota’s 16,000. Wisconsin’s prisons guzzle state funds at twice the rate of next door: $150 is spent for every Wisconsinite to $74 per Minnesotan. A growing body of elderly lifers with soaring medical bills will push costs much higher. At times, state funding for prisons—about $1.2bn, or $38,000 per prisoner yearly—exceed spending on Wisconsin’s university system.

Nor has Wisconsin’s tougher regime obviously limited crime any better than its neighbour’s laxer one: rates are similar in each state (violence is somewhat lower in Minnesota). Yet Scott Walker, Wisconsin’s governor, knows that many voters like toughness whatever the actual outcomes. “He’s running on fear” observes Mr Amphy. Mr Walker attacks his Democratic opponent, Tony Evers, for saying prison numbers should come down.

Once out of office, even formerly tough guys quickly grasp how big prison populations are harmful. Typical is Mr Wall, “a cop of 30 years” who fiercely favoured harsh sentencing before he ran Wisconsin’s prisons. Now he wants “change in all elements” such as softening sentences, easing parole, more help to treat mental health and offer job skills. “If I can get the message, anyone can get it”, he says.

Tommy Thompson, a Republican governor for 14 years, also regrets overseeing a boom in prisoners. “We warehouse them. Constantly building prisons is not the way to go. Minnesota is not, and their crime is no worse than ours”, he says. He is keen to lead a reform programme, but says state politicians “are afraid as hell” of change. Mr Walker won’t even visit his own prisons, declaring there’s “no value” in doing so.

What could reform include? Mr Thompson wants vocational studies and early release for perhaps one-third of current prisoners. Kelly Mitchell, of the Robina Institute at the University of Minnesota, says various combined efforts are needed. A start would be setting up an independent sentencing commission like one she used to run in Minnesota. It advises legislators on how any new law would affect prison numbers and its cost to taxpayers. Even tough-on-crime legislators soon turn more cautious when obliged to include such information in their bills, she says.