President Donald Trump and Attorney General Jeff Sessions weren’t kidding when they promised to ramp up the war on drugs.

On Friday, Sessions took his first big step as attorney general to escalate America’s drug war: He rescinded an Obama-era memo sent out by then-Attorney General Eric Holder in 2013, which told federal prosecutors to avoid charges for low-level drug offenders that could trigger lengthy mandatory minimums.

Sessions’s new memo instructs prosecutors to go in the exact opposite direction and charge even low-level offenders with the most severe penalties possible. It says that “prosecutors should charge and pursue the most serious, readily provable offense,” calling this concept “a core principle” of the Justice Department.

Holder’s memo didn’t leave prosecutors totally powerless. It included exceptions, for example, for offenders who were part of a large-scale drug trafficking organization, gang, or cartel. But that apparently wasn’t enough for Sessions.

Sessions’s latest move gives some of the most powerful actors in the criminal justice field even more power to impose long drug sentences. Prosecutors have the discretion to decide what someone gets charged with — or if a defendant is charged at all. Some prosecutors, such as former Brooklyn District Attorney Kenneth Thompson, have used this power to refuse to charge certain low-level drug offenders. Sessions is now telling federal prosecutors that they should no longer do that, and that they should, as a general matter, charge defendants with the most stringent penalties possible.

Sessions’s memo only applies to federal prosecutors. Municipalities and states, which oversee the great majority of the criminal justice system, will still be able to dictate their own policies. Still, the federal criminal justice system is quite large — given that it houses nearly 200,000 prisoners — and Trump and Sessions seem keen on making it even larger.

To some degree, this is hardly surprising; Trump and Sessions have long spoken about how they are “tough on crime” and, therefore, support stringent prison sentences for criminals. But this means that, at least in the next four years, we can expect America to amp up its federal war on drugs once again.

Trump and Sessions have fashioned themselves as “tough on crime”

No one can say Trump and Sessions didn’t warn us.

In 2015, Trump outright told MSNBC that he’s “tough on crime.” He praised Vice President Mike Pence for increasing mandatory minimum sentences for drug crimes as governor of Indiana. He falsely claimed that the murder rate is at a 45-year high when it’s actually near a historical low. And he said police should be more aggressive than they are today, particularly by using the controversial “stop and frisk” strategy that a court struck down in New York City because it was used to target minority Americans.

Sessions, a former federal prosecutor, has similarly taken a hardline view on crime and drugs. In his last year in the Senate, he was key in killing a criminal justice reform bill that would have relaxed prison sentences for low-level drug offenders. He criticized police reforms led by the Obama administration during a November 2015 Senate hearing called “The War on Police.” And he said that “good people don’t smoke marijuana” while advocating against pot legalization.

Trump and Sessions’s “tough on crime” push defies some of the evidence we’ve seen over the past few years, which has found that tougher criminal justice policies aren’t very effective.

For example, a 2014 study from Peter Reuter at the University of Maryland and Harold Pollack at the University of Chicago found there’s no good evidence that tougher punishments or harsher supply-elimination efforts do a better job of driving down access to drugs and substance misuse than lighter penalties. So increasing the severity of the punishment doesn’t seem to do much, if anything, to slow the flow of drugs.

Similarly, a 2015 review of the research by the Brennan Center for Justice estimated that more incarceration explained only about 0 to 7 percent of the crime drop since the 1990s, while other researchers estimate it drove 10 to 25 percent of the crime drop since the ’90s. That’s why criminal justice experts now emphasize that there are better ways, from new policing tactics to more stringent alcohol policies, to bring down crime without resorting to longer prison sentences.

Trump and Sessions, however, have stuck to their prior beliefs about policing and incarceration. Now that they’re in power, they have an opportunity to undo the big policy shift that President Barack Obama’s administration mounted on these issues.

Trump and Sessions now have a chance to undo the reforms Obama enacted

Although it was never a big part of Obama’s campaigns or speeches, his administration did take a number of steps to pull back the war on drugs. It publicly spoke of the opioid epidemic as primarily an issue of public health, not criminal justice. (Obama’s “drug czar,” Michael Botticelli, repeatedly said that “we can’t arrest and incarcerate addiction out of people.”) It shifted anti-drug spending to emphasize public health programs, like drug treatment, as much as approaches focused on criminal justice and national security.

Holder’s memo was an early part of this push, emphasizing that the old war on drugs had gone too far in punishing low-level offenders.

Beyond that, Obama also granted clemency to more federal convicts — mainly drug offenders — than any president since Harry Truman.

All of this had the support of experts and the public, who widely see a public health approach as the right way to deal with drug problems like the opioid epidemic. To put into context how much help is needed, consider this statistic: According to a 2016 report by the surgeon general, just 10 percent of the people with a drug use disorder get specialty treatment. The report found that the low rate was largely explained by a shortage of treatment options, including medication-assisted treatment.

Yet by rescinding Holder’s memo, the Trump administration is beginning to undo the work of its predecessors. But the administration could go further: It could shift anti-drug spending to focus on law enforcement and interdiction than public health programs, although it would need congressional approval to do this. It could encourage legislation or enforce more executive actions that make police and prosecutors even more aggressive than they are today.

And the Trump administration could speak to the opioid epidemic as a criminal justice issue instead of a public health crisis, encouraging policymakers to reemphasize “tough on crime” tactics for drugs. In fact, Sessions has already begun doing that: “Our nation needs to say clearly once again that using drugs is bad,” he told law enforcement in a speech earlier this year. “It will destroy your life.”

Based on Sessions’s latest memo, this rhetoric, along with executive actions to match it, is what we can expect from the Trump administration over the next few years. The war on drugs may soon come roaring back.

Watch: The opioid epidemic, explained