House Democrats are investigating the Trump administration’s retreat from federal investigations of unconstitutional policing practices, asking the Department of Justice for a number of internal documents on civil rights probes of law enforcement since the end of the Obama presidency.

A letter to Attorney General William Barr ― signed by Reps. Jerrold Nadler (D-N.Y.), chairman of the House Judiciary Committee, and Karen Bass (D-Calif.), chairwoman of the Congressional Black Caucus, amongst others ― indicates that lawmakers are examining why DOJ has “sharply curtailed its statutory role in identifying and eradicating civil rights abuses by law enforcement.”

Use of excessive force by police “presents a crisis of trust,” and DOJ’s retreat from “pattern or practice” cases runs “the risk of undermining federal oversight authority in this space,” the letter states.

While the Justice Department has continued bringing cases at a relatively steady clip against individual police officers who commit egregious and well-documented civil rights abuses, its civil rights division has backed away from investigating police departments that engage in unconstitutional practices on a systemic level. Under then-Attorneys General Eric Holder and Loretta Lynch, the Obama-era civil rights division investigated police departments in cities like Chicago, Cleveland, Newark, Baltimore and Ferguson, Missouri, where a policing-for-profit scheme built up mistrust between the community and law enforcement that exploded on the streets after an officer killed 18-year-old Michael Brown. But that all changed under Jeff Sessions, President Donald Trump’s first pick for attorney general.

Sessions subscribed to a “few bad apples” view of police abuse and didn’t think the federal government should play a role in reining in unconstitutional policing on the local level. He argued that DOJ’s pattern-or-practice investigations ― brought under a law passed in the wake of the police beating of Rodney King ― “undermine respect for police officers” and create an impression that an “entire department is not doing their work consistent with fidelity to law and fairness.” Shortly after he became attorney general, Sessions claimed that DOJ’s in-depth examinations of police abuse in Chicago and Ferguson were “pretty anecdotal, and not so scientifically based,” even as he conceded that he had not actually read the reports.

After Trump took office, the Justice Department unsuccessfully tried to back out of a deal reached with the city of Baltimore during the Obama administration and moved to block police reform in Chicago. Sessions initiated a review of all of DOJ’s work on police reform to determine if it promoted “officer safety and morale,” respected “local control of law enforcement” and did “not impede recruitment and training of officers.” In his final hours as attorney general this past November, he signed a memo that sharply curtailed the Justice Department’s ability to rein in unconstitutional policing practices through consent decrees.

Under Sessions, the Justice Department also effectively killed a less adversarial version of police reform led by its Office of Community Oriented Policing Services (COPS). The Collaborative Reform Initiative, which began during the Obama administration, was intended to encourage local police forces to voluntarily enter into a cooperative reform process. The program is now about police reform in name only: The money Congress allocated to the program has been funneled to law enforcement organizations themselves for public safety and crime reduction goals.

Christy Lopez, a former career official in the civil rights division who led much of DOJ’s policing work during the Obama administration, said it was a “good sign” that House Democrats were looking into how the Trump administration is handling pattern-or-practice investigations.

“There are so many issues and problems they could address right now, and the fact that they chose to address this one indicates how important it is, I think, not only to people in Congress but their constituents across the country,” Lopez told HuffPost. “It’s a great first step, but it really is just that. Hopefully, it will set the stage for similar pressure.”

A significant number of employees in the civil rights division’s special litigation section who were working on police investigations have departed since the Trump administration began.

The Trump administration is shunning congressional oversight in a number of areas, so the timeline of the investigation into DOJ’s police reform practices is unclear. A Justice Department spokeswoman did not respond to a request for comment.