Jeff Sessions, Donald Trump's pick to become the nation's top lawman, could dramatically shift the federal government's approach to police reform by choosing not to pursue the aggressive investigations of local departments that have expanded in the Obama administration.

The Alabama senator, who will appear before his colleagues on the Senate Judiciary Committee Tuesday for the start of confirmation hearings, has expressed skepticism of the Justice Department's focus on forcing change on police departments — a view shared by Trump, who has complained of a "war on police," and has opposed federal interference in local law enforcement.

That would deal a blow to the legacy of President Obama, who has been touting his attempts to reform American policing, including the most aggressive pursuit of systemic misconduct since the federal government won broad investigative powers more than two decades ago.

In a November 2015 Senate hearing called "The War on Police," Sessions, a former federal prosecutor, tore into the Justice Department's Civil Rights Division, which under Obama has taken a more forceful approach to investigating systemic abuses of police power. He accused the department of overstepping its authority and undermining officers.

"There is a perception, not altogether unjustified, that this department, the Civil Rights Division, goes beyond fair and balanced treatment but has an agenda that's been a troubling issue for a number of years," Sessions said.

Sessions has also criticized consent decrees, the Justice Department's main tool to impose reforms. He once called them "one of the most dangerous, and rarely discussed, exercises of raw power" and "an end run around the democratic process."

He is in many ways the political opposite of the attorneys general who led Obama's reform agenda, Loretta Lynch and Eric Holder. Both took bold approaches to reform efforts, sending the Civil Rights Division into cities where police killings of suspects triggered unrest and where cops had been accused of heavy-handed enforcement.

Under Lynch and Holder, the division launched investigations of more than two dozen departments and forced 14 of them into expensive, court-enforced consent decrees aimed at improving a variety of ways cops dealt with citizens, including use of force, stops and searches, and discriminatory enforcement. The division has pending investigations into another six departments, including Chicago's and Baltimore's.

Related: Justice Department Finds Baltimore Police Practices Are Racially Biased

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The Justice Department won the power to do these investigations in 1994, after the beating of Rodney King in Los Angeles, and the riots that followed the officers' acquittal, exposed institutional failures by the department. Under Bill Clinton and George W. Bush, the Justice Department used its new powers relatively sparingly, negotiating consent decrees with the LAPD and five other police departments.

Obama made broader use of that power, particularly as fatal use of force by police in New York, Ferguson, Missouri and Cleveland triggered public unrest. The crackdown also triggered a backlash by police and their supporters, who said it was contributing to a slowdown in enforcement, a rise in crime and attacks on officers.

Trump campaigned on that issue, and Sessions, one of his earliest Senate supporters, joined him.

Related: U.S. Finds Pattern of Biased Policing in Ferguson

Police advocates, legal analysts and former members of the Civil Rights Division say Sessions could change the Justice Department's approach by being more choosy in what departments to go after, and how hard to press for changes. That could mean pursuing fewer investigations, negotiating fewer consent decrees and taking a less stringent approach to those already underway.

But even as he has criticized the Obama administration, Sessions has stressed that the Civil Rights Division, and community policing efforts, still have an important place in American law enforcement.

Laurie Robinson, a former Justice Department official who oversaw grants for police reform efforts under Clinton and Obama, and who has worked with Sessions on federal "Weed and Seed" programs, said she expected Sessions to continue to back such voluntary efforts.

Sessions could find that middle ground in a program under the Office of Community Oriented Policing Services that provides technical assistance to departments that ask for help, Robinson said.

Robinson also served as a co-chair for Obama's White House Task Force on 21st Century Policing, which published a long list of reform proposals in March 2015. There are many items in that report that Sessions would probably recoil from, including the requirement that outside agencies investigate shootings by police. "But I guess that many of the things in many of our broader principals he would support," Robinson said.

James Pasco, executive director of the National Fraternal Order of Police, one of many police organizations that endorsed Trump, said he's known Sessions for two decades and would welcome his confirmation.

"He's always been a very inclusive and collaborative legislator and expect that same type of inclusion as attorney general," Pasco said.

Sessions has taken a hard line on other policies that impact local police: the legalization of marijuana and allowing authorities to confiscate people's property even if they haven't been convicted of a crime. His call for stricter immigration enforcement has led to speculation that he could pressure local police to target people in the country illegally.

"Reform can mean changing what police do, and how police do it," said Seth Stoughton, a University of South Carolina law professor and former officer who studies police regulations.

Many see the pending Chicago investigation, which focuses on police use of force, as a potential bellwether for how Sessions would handle reform. It is the Civil Rights Division's largest ever probe of a local department, and is expected to be completed shortly. But the next attorney general would have to decide what to do with the findings, including whether to negotiate a settlement with the city.

Related: Justice Department to Investigate Chicago Police After Laquan McDonald Death

"Chicago is going to be a real testing ground," said William Yeomans, who worked for 24 years in the Civil Rights Division. "If you're really going to be serious about large structural changes to a police department, going to court and entering a consent decree is really the only serious way to go about it."

Another former Civil Rights Division official, Jonathan Smith, said reforms not only protect citizens, but also officers, because it improves relationships between the two. "The idea that we can have one or the other, constitutional policing or public safety, is false," he said. "We need both to work."

Public support of police has increased in the past year, with three-quarters of American saying they have a great deal of respect for officers, according to a recent Gallup poll.

Ron Serpas, who was superintendent of the New Orleans Police Department when it came under a consent decree in 2013, said he saw firsthand how the Justice Department could "overreach" in forcing reforms. But Serpas, who now teaches criminal justice at Loyola University, said consent decrees are still an important tool for some departments.

"You can't do aggressive law enforcement in a community without its support and trust," Serpas said.