Under President Barack Obama, the Justice Department used its oversight authority to push for fundamental changes in the way local law-enforcement agencies interact with the communities they serve. Now under President Trump and Attorney General Jeff Sessions, the federal government seems poised to pull back on that kind of enforcement — pleasing police officers but worrying activists.

Obama’s Justice Department greatly expanded both the number and scope of “consent decrees,” legally enforceable agreements with police departments on issues such as racial discrimination, use of force and unlawful stops and seizures. The Obama administration used the consent decree process to push for changes in places such as Chicago and Ferguson, Missouri, after high-profile killings by police.

The Justice Department’s authority to investigate police departments stems in part from an earlier high-profile incident of police violence: the 1991 Rodney King beating in Los Angeles. Congress later passed the Violent Crime Control and Law Enforcement Act, which, among other provisions, tasked the Justice Department with investigating systematic misconduct in law enforcement agencies. To do so, the Justice Department identifies police departments that have a “pattern or practice” of violating the constitutional rights of a city’s residents and then either reaches voluntary memorandums of agreement outlining how the departments will address the problems or, if those negotiations fail, goes to court to pursue a legally binding consent decree. In cases of court-ordered consent decrees, judges often appoint monitors to make sure the changes are carried out.

Different administrations have used that power differently. According to a Justice Department report, in the period from 1997 through 2008 — which encompasses Bill Clinton’s second term and all of George W. Bush’s presidency — the Justice Department came to a little more than one police reform agreement (voluntary or court-ordered) per year. Under Obama, however, the Justice Department issued 24 reform agreements, averaging three per year. That rate contrasts most significantly with Bush’s second term: no reform agreements were issued from 2005 through 2008.

Obama’s Justice Department, under both Eric Holder and Loretta Lynch, also broadened the scope of potential violations. In addition to excessive force, unlawful stops and seizures, and racial bias, the Obama Justice Department took some police departments to task for gender bias (including inaccurate reporting of sexual assault) and bias against people with disabilities. The investigations were part of a larger set of police reform efforts pursued by Obama, including programs such as the White House Police Data Initiative, which sought to increase transparency and make police data accessible to the public.

Under Trump, however, the Justice Department appears likely to conduct fewer such investigations. During his confirmation hearings in January, Sessions voiced skepticism about consent decrees, which he said “undermine the respect for police officers and create an impression that the entire department is not doing their work consistent with fidelity to law and fairness.” In a speech in February, Sessions said his department would “pull back” on investigations of police departments, and he hasn’t said whether he will continue the consent decree process that his predecessor began in Chicago.

“We need to help police departments get better, not diminish their effectiveness, and I’m afraid we have done some of that,” Sessions told the National Association of Attorneys General, according to the Chicago Tribune. The Justice Department declined to comment.

Chiraag Bains, a former senior official in the Justice Department’s civil rights division under Obama, said in an interview that if Trump and Sessions return to the lighter enforcement approach of the Bush years, police reform efforts will lose momentum. “If that’s the world Sessions wants to go back to, I think that there would be serious consequences for both citizens and law enforcement officers,” Bains said.

But police officers are likely to greet any pullback more warmly. Justice Department-mediated police reforms tend to be unpopular with police officers, and studies have found that consent decrees had short-term, but dramatic, negative effects on police morale.

“If Sessions is saying he wants to stop [consent decrees] — good,” said Tony Barksdale, former deputy commissioner of operations for the police department in Baltimore, which entered into a consent decree with the Justice Department in January. “It handcuffs the cops, but what about the criminals?”

Studies have found that consent decrees are effective in some cases and not in others. A study of the first Justice Department consent decree, issued in Pittsburgh in 1997, found that it was successful in altering the long-term behavior of the department. A similar study examined the Los Angeles Police Department after a 2001 consent decree and found major improvements in the department and the city’s perception of its policing. On the other hand, a study of the New Jersey State Police after a 1999 consent decree showed no progress in eliminating racial disparities in traffic stops on the New Jersey Turnpike. An author of that study, Columbia University Professor Jeffrey Fagan, said in an interview that consent decrees often don’t fix the underlying constitutional problems: “On balance, you can tweak internally (management, procedures, hardware, training, discipline), but those tweaks don’t seem to produce big changes externally.”

Because every law enforcement agency and reform agreement is different, coming to definitive conclusions about the effectiveness of consent decrees in general is difficult. Some departments have complained about the expense of carrying out changes, and there are questions about whether the changes to police behavior remain after the agreements expire. Cities can have problems re-emerge after initial progress has been made: Cleveland’s police department has been the subject of two police reform agreements — one that expired in 2005 and a second that started in 2015.

Bains said the Justice Department has gotten better at making reforms stick. As an example, he pointed to the Obama’s administration’s decision to switch from using mostly voluntary agreements to using court-enforced consent decrees. “The experience of DOJ is that consent decrees are more likely to yield … lasting change,” Bains said. Monitors, whose job it is to make sure that police departments fulfill the terms of the agreements, now lean on quantitative benchmarks that must be met before the consent decree can be resolved. Bains said these outcome measures better determine whether the police department’s policies have made significant change.

It isn’t yet clear how far Sessions will go in reversing the Obama administration’s efforts. There are 19 police reform agreements currently in place, and Sessions has not described his policy toward them beyond saying at his confirmation hearing that he will enforce agreements unless they are changed. If Sessions pulls back on enforcement of existing police reform agreements, nearly half of the agreements ever reached could lose their potency. If Sessions ceases to pursue new investigations but continues to enforce existing ones, the number of active agreements will be greater than during George W. Bush’s second term in office.