For the past few years, criminal justice policy has widely been considered an area ripe for reform from Democrats and Republicans. They want to make the system less punitive and pull back mass incarceration — a rare show of bipartisanship in an increasingly polarized political climate.

Then came Donald Trump.

On the campaign trail, the Republican presidential candidate has been somewhat of an enigma on criminal justice issues. Trump's website includes no platform on criminal justice issues. Reform advocates have long complained to me that they have trouble getting in touch with his campaign to get an idea of his views. And despite some vague remarks here and there, he's almost never talked at length about what he thinks about criminal justice issues. (His campaign didn't get back to me for this piece.)

But there are some big clues about what kind of policies President Trump would pursue — and none of them are good for reform.

To gauge this, I looked at Trump's comments over the past few decades, particularly his 2000 book, The America We Deserve, which has perhaps his clearest statements on criminal justice policy. I also looked at Trump's advisers — the people most likely to influence his thinking on criminal justice issues. And I looked at the few comments Trump has made on the campaign trail regarding these issues.

A clear trend emerged: Trump would very likely be "tough on crime" — he would very likely back tougher prison sentences and invasive policing practices, and would likely continue the more punitive aspects of the war on drugs.

To some degree, this isn't too surprising: Trump is an authoritarian strongman, so it makes sense that his approach to this issue, as with immigration and national security, would be to act as tough as possible. And he lived in New York City in the 1970s, '80s, and '90s, when the city was engulfed by violent crime — a time period that likely influenced his views.

Still, it shows that for all the discussion in media and politics about bipartisan criminal justice reform, the candidate for president on one side appears far from interested in making the criminal justice system less punitive. Here are three major pieces of evidence that demonstrate this point.

Trump's 2000 book checks off all the "tough on crime" positions

Trump's 2000 book, The America We Deserve, offers the clearest view into his criminal justice positions — and they're unquestionably "tough on crime."

Trump warns about an incoming crime wave "early in 2000." (This never happened; crime has steadily dropped since the mid-1990s.) He dismisses social contributors to crime — particularly "poverty, lack of opportunity, or early childhood mistreatment" — as excuses, arguing that such explanations for crime enable "soft" policies that aren't tough enough to make US streets safe. And he favors "a zero-tolerance policy," lengthy prison sentences, and aggressive police tactics.

Trump's thesis explicitly embraces "tough crime policies":

Tough crime policies are the most important form of national defense. Government's number-one job is to ensure domestic tranquillity [sic], and that means tranquilizing the criminal element as much as possible. Aggressive anticrime policies are the best social program, because they allow citizens in all neighborhoods, and especially the tougher ones, to live and work in a safe environment. They also protect children from the predatory mob that brutalizes them at every turn.

He calls for putting more people in prison:

According to the bipartisan group Council on Crime in America, on any given day there are about 1.5 times more convicted violent offenders out on the streets on probation or parole than are behind bars.

Clearly we don’t have too many people in prison. Quite the contrary.

Meanwhile, the rest of us need to rethink prisons and punishment. The next time you hear someone saying there are too many people in prison, ask them how many thugs they’re willing to relocate to their neighborhood. The answer: None.

He also asserts that people are in prison because they all deserve to be there:

I could understand the argument that we have too many people in prison if the police were rounding up innocent people and locking them away. But that's not the case. For the most part, you have to be a longstanding criminal to qualify for jail. This will come as news to our opponents in this debate.

He defends "broken-windows policing" and "stop and frisk" tactics, both of which have been criticized, and the latter ruled unconstitutional, because they're used by police to harass minority residents in particular and aren't even proven to reduce crime:

This attitude is working wonders for all our citizens and especially for those who had been abandoned by previous feel-good administrations.

What has New York been doing right?

[New York City Mayor Rudy] Giuliani's first police commissioner, William Bratton, was the first to see that the job of the police wasn't to sit around waiting to answer 911 calls and hope that the person on the other end of the line was still breathing. It was Bratton who reoriented the police from being reactive to being proactive. He targeted patrols and crime prevention on "hot spots." He insisted on treating minor crimes — subway cheaters and minor vandals — as precursors to more serious crimes and potential signals to others that anything goes.

In other words, the word went out: We're not going to let the little stuff slide. That has made the big difference.

He argues that the death penalty deters crime — a position the research doesn't bear out:

I can't believe that executing criminals doesn't have a deterrent effect. To point out the extremely obvious, 100 percent of the people who are executed never commit another crime. And it seems self-evident (we can't put numbers to this) that a lot of people who might otherwise commit a capital crime are convinced not to because they know there's a chance they could die for it. Not all crime is irrational.

And he states that lethal injection is "too comfortable a way for these criminals to go," adding that capital punishment is more civilized than not executing murderers:

Civilized people don't put up with barbaric behavior, such as dragging people to death behind pickup trucks. Would it have been civilized to put Hitler in prison? No— it would have been an outright affront to civilization. The same is true of criminals who prey on innocent men, women, and children. By their acts they have not only rejected civilization but also declared war on it. And I don't care if the victim is a CEO or a floor sweeper. A life is a life, and if you criminally take an innocent life you'd better be prepared to forfeit your own.

The consistent theme in Trump's stated views is that criminals need to be punished as harshly as possible — typically through the view of "an eye for an eye" — to keep such criminals off the streets and deter future ones.

But the empirical research and history show severity of punishment does little to deter crime. Studies of mass incarceration have found, for example, that putting more people in prison reached the point of diminishing returns long ago. There are only so many serious, repeat offenders to incapacitate in prison, and long prison sentences tend to capture a lot of people, particularly older folks, who are very unlikely to reoffend, since people tend to age out of crime after their 30s.

This is why criminal justice reformers and experts widely believe it is possible to shorten prison sentences without risking significantly more crime. But Trump flatly rejects those views in The America We Deserve.

Trump's campaign rhetoric is all "tough on crime" 

Now, Trump's book is from 2000. So you might think it's possible that he has changed his views over the years, especially after that crime wave he predicted never occurred. But while he's been short on specifics, his campaign rhetoric suggests he's still "tough on crime."

In August 2015, during an appearance on MSNBC, Trump said "we have to get a lot tougher" on violent offenses and if police "do their job the way they know how to do it, they will stop the onslaught of crime in this country." He doubled down on this view in November 2015, during another appearance on MSNBC, saying, "I'm tough on crime. … You look at what's going on in the inner cities right now, it's unbelievable. … It's like the Wild West."

In an August 2016 interview with Bill O'Reilly, Trump reiterated his support for "tough police tactics" when asked about how to bring down crime and murder rates in Chicago.

"By being very much tougher than they are right now," Trump said. "They're right now not tough. I could tell you this very long and quite boring story. But when I was in Chicago, I got to meet a couple of very top police. I said, 'How do you stop this? How do you stop this? If you were put in charge — to a specific person — do you think you could stop it?' He said, 'Mr. Trump, I'd be able to stop it in one week.' And I believed him 100 percent."

He added, "He wants to use tough police tactics, which is okay when you have people being killed."

In September 2016, Trump got more specific, saying he would expand the controversial "stop-and-frisk" strategy previously used by the New York City Police Department — until a court deemed the practice unconstitutional. "I would do stop-and-frisk," Trump said. "I think you have to. We did it in New York. It worked incredibly well."

Despite Trump's claims, studies show stop-and-frisk did not have a significant impact on crime in New York City — and instead worsened police-community relations, particularly among black residents who were much more likely to be stopped despite being less likely to have contraband when they were searched.

At his May 2016 speech accepting the National Rifle Association's endorsement, Trump also criticized President Barack Obama and Hillary Clinton for supporting criminal justice reform — by exaggerating its effects. He claimed:

Obama is even releasing violent criminals from the jails, including drug dealers, and those with gun crimes. And they're being let go by the thousands. By the thousands. … Obama pushed for changes to sentencing laws that released thousands of dangerous, drug-trafficking felons and gang members who prey on civilians. … This is Hillary Clinton's agenda, too — to release the violent criminals from jail. She wants them all released. She wants people released that you wouldn't want to walk on the street with, you wouldn't want to look at.

In his July 2016 speech accepting the Republican nomination for president, Trump also warned of rising crime levels over the past couple years (even though nationwide crime figures for the past two years are not yet available). He blamed this supposed rise in crime on the Obama administration's "rollback of criminal enforcement," again suggesting that the criminal justice reform the White House has pursued is making America less safe.

Trump has also defended police standing in opposition to Black Lives Matter protests over police shootings and brutality. At a debate in February 2016, he argued that police are "absolutely mistreated and misunderstood." In the context of Black Lives Matter, the signal here is clear: Trump tends to side with police in disputes about excessive use of force.

So while many lawmakers, including the Obama administration, are talking up treating the opioid epidemic as primarily a public health crisis, Trump is focusing on how law enforcement can stop heroin coming from Mexico. (Still, Trump has acknowledged that America needs to increase funding for drug abuse treatment.)

Trump has said he doesn't think kids should be tossed in prison for marijuana use. And he acknowledged that as some states are legalizing, "it's sort of hard to say that you're on one side of the border and you go to jail, and you're on the other side and you can go into a store and buy it. So there's going to be changes made there." But he said, "I think that maybe the dealers have to be looked at very strongly" — suggesting that he thinks some drug offenses should still be punished harshly.

Again, most of these statements are vague. But coupled with Trump's comments in his 2000 book, it paints an overall picture of a "tough on crime" attitude.

Trump has surrounded himself with criminal justice hard-liners

Now, maybe it is true that Trump is predisposed to be tough on crime. But perhaps it's not an issue he cares much about now, or maybe it's something he could be persuaded on. That's where his advisers could come in — maybe they could point him to the large body of evidence that shows "tough on crime" policies haven't really worked.

Except Trump has surrounded himself with people who are also "tough on crime."

Take New Jersey Gov. Chris Christie, who is a close adviser for Trump and often named as a possible candidate for Trump's attorney general. When asked about police, Christie has given a very consistent answer: He does not approve of Black Lives Matter and the broader protests over police use of force. In a debate last year, Christie said, "[W]hen I'm in the Oval Office, police officers will know that they will have the support of the president of the United States."

Christie has taken a softer view toward the heroin crisis and drug abuse and has argued for helping ex-offenders find jobs. But he also said he would crack down on states legalizing marijuana — by shutting down retail outlets. He also said that, as a prosecutor, he would have arrested NFL player Laremy Tunsil after Tunsil smoked marijuana in a video.

Beyond Christie, Trump is also close with Sen. Jeff Sessions, who has played a key role in stalling the Senate's criminal justice reform. And Trump campaigned with Maine Gov. Paul LePage, who vetoed a bill that would have increased access to the opioid overdose antidote naloxone, because he worried that saving people from overdoses would send the wrong signal to drug users.

Meanwhile, it's hard to find anyone close to Trump who strongly backs criminal justice reform. The Koch brothers, the biggest pushers of reform on the right, clearly dislike Trump.

Once again, the signs point in a single direction: Trump is "tough on crime," and he's surrounded himself with people who are "tough on crime," too.

The bottom line: Trump could be very bad for criminal justice reform

It seems like a fool's errand to try to evaluate Trump's policy positions, given that so much of his campaign is built on pure bluster and showmanship. But Trump is now a single election from potentially becoming president of the United States, making his views, as difficult as they may be to discern at times, all the more important.

Could Trump alone enforce aggressive policing tactics and cause incarceration rates to rise again after a few years of slight declines? Probably not. As Trump's campaign has acknowledged, most policing policies happen at the state and local level — that's where the great majority of America's police departments are. Prisons are the same way: State prisons and local jails hold about 87 percent of the incarcerated population. Federal policy can influence all of this with funding incentives and grants, but much of that effect is on the margins.

But criminal justice policy is often framed as one of the few areas where serious reform legislation could get done — with support from Republicans like House Speaker Paul Ryan and Democrats like President Obama. As it stands, the only obstacle in the way of federal legislation seems to be election-year politics. But after 2016, it's widely expected that something really can get done.

Trump could change that dynamic: In the White House, he could singlehandedly veto any attempt at reform. And based on his record, he very likely would.