Jeff Sessions (R-Ala) has been dubbed by a newsmagazine as the Senate’s “anti-immigration warrior,” based largely on his successful opposition to any legislative efforts to reform the U.S. immigration system. (Molly Riley/AP)

As a senator from Alabama, Jeff Sessions has vigorously opposed any efforts to reform the U.S. immigration system in ways that might benefit those in the country illegally. He has advocated tempering even legal immigration, fearful that people from other countries might take Americans’ jobs.

Sessions (R), President-elect Donald Trump’s pick to be the next attorney general, will face no shortage of questions at his confirmation hearing starting Tuesday about his alleged past racist comments, his prosecution of civil rights activists, and his views on voting rights and same-sex marriage. But civil liberties advocates say Sessions’s views on immigration concern them just as much because of the role the Justice Department plays in dealing with those who come to the United States from other countries, and because of the constitutionally questionable policies Trump has suggested that Sessions’s Justice Department would likely implement.

“I think it’s disturbing to contemplate what he would do as attorney general,” said Cecillia Wang, director of the ACLU Immigrants’ Rights Project.

Trump has proposed establishing a registry of Muslims and imposing a ban on their immigration to the United States. Sessions’s Justice Department could try to offer him legal footing to do so, and then defend those policies from the legal challenges they are certain to face.

(Thomas Johnson/The Washington Post)

Karen Tumlin, legal director of the National Immigration Law Center, said she fears that Sessions might even “not feel it was a responsibility of the Justice Department to protect the civil rights of Muslim Americans in this country.”

“It’s not because we quibble on policy,” she said of why she does not support Sessions’s nomination. “It’s because I quibble with the nation’s top lawyer not protecting equality in our country.”

Sessions proposed as a senator a bill that would impose a five-year mandatory minimum prison term on those found to have re-entered the country illegally. Advocates fear he might now direct prosecutors to bring such cases more vigorously, and seek stiffer penalties. In fiscal year 2015, the average sentence for such an offense was just 16 months, according to data from the U.S. Sentencing Commission.

The Trump administration has suggested it will rescind President Obama’s executive action that allows people who came to the United States as children to receive work permits and a reprieve from possible deportation. Advocates fear Sessions might use those people’s information now to deport them. The National Immigration Law Center has advised those who do not use the program to not apply for it, because that would give authorities information on those in the country without proper documentation.

Many people, of course, would support a crackdown on illegal immigration. Trump, whose views mirror those of Sessions, was notably endorsed by the unions representing America’s Border Patrol and Immigration and Customs Enforcement agents.

“Our officers come into daily contact with many of the most dangerous people in the world — cartel members, gang members, weapons traffickers, murder suspects, drug dealers, suspects of violent assault — yet ICE Officers are unable to arrest or are forced to release many of the most dangerous back into U.S. communities due to unscrupulous political agendas and corrupt leaders,” the Immigration and Customs Enforcement union said in a statement on the Trump website.

Sessions’s position on the topic also is no secret. Politico last year dubbed Sessions the Senate’s “anti-immigration warrior,” based largely on his successful opposition to any legislative efforts to reform the immigration system. Peter Nunez, a former U.S. attorney in the Southern District of California who now serves as chairman of the board for the Center for Immigration Studies, which advocates reducing immigration levels, said Sessions has from his days as a federal prosecutor been “shocked and appalled” by the border security problems. Nunez said he hopes Sessions will not just crack down on illegal reentry, but prosecute employers who give jobs to illegal immigrants.

(Bastien Inzaurralde/The Washington Post)

“Based on his record in the Senate, and based on what the president-elect has said, I would take it that he is going to do his best to increase and improve border enforcement,” Nunez said.

Sessions has opposed even those in his own party.

In 2007, for example, he spoke out on the Senate floor against a George W. Bush-backed bill that would have offered legal status to millions and improved border security, drawing on his experience as a federal prosecutor as he urged fellow legislators to vote down the measure.

“I don’t think there’s any other person in this body that has personally prosecuted an immigration case but this senator,” he said, gesturing to himself. “I have done that years ago. I just say that I’m familiar with the process. I’m familiar with the system and the difficulties, how overwhelmed it has been, and why it is not working.”

The case, according to another Sessions speech, occurred when he was an assistant U.S. attorney and involved stowaways on a ship. The immigration reform bill ultimately died, and when the Senate again took up the issue with a bipartisan bill in 2013, Sessions again led the charge to kill it.

Armand DeKeyser, Sessions’s former chief of staff, said Sessions’s views on immigration seemed to have originated in the late 1990s, when he went on a “listening tour” of his home state. Several city police chiefs and county sheriffs noted that the U.S. Border Patrol was filling their jails with undocumented Mexican immigrants, and they wanted to know how they would be reimbursed for the upkeep.

“We were not aware of this problem until then,” said DeKeyser, who also worked for Sessions when he was U.S. attorney and state attorney general. “We didn’t have any idea it was that big a problem. We were surprised at the numbers.”

In the years that followed his listening tour, Sessions came to believe that the undocumented immigrants in rural Alabama were taking the jobs of other residents. He advocated against even legal immigration, arguing that anyone coming to the United States should benefit the citizens already here.

“What sense does it make to continue importing millions of low-wage workers to fill jobs while sustaining millions of current residents on welfare?” he wrote in a 2015 memo called the Immigration Handbook for the New Republican Majority. “Indeed, the same companies demanding a large boost in foreign labor are laying off American workers en masse.”

At a 2006 congressional hearing, Sessions pushed the controversial position that an entire group of people wouldn’t thrive in America.

“Fundamentally, almost no one coming from the Dominican Republic to the United States is coming because they have a skill that would benefit us and would indicate their likely success in our society,” he said.

Not unlike the man who wants him to serve as attorney general, Sessions seems to take a populist view of immigration reform. In a 2007 speech, he derided his colleagues who conceived of the immigration reform bill as “masters of the universe,” alleging they secretly hatched a plan that did not take into account the view of those actually working to deal with illegal immigrants.

“They didn’t invite anybody from the border patrol in there that’s actually working the borders or agents from ICE,” Sessions said. “They had, of course, direct and regular contact with big business. They had direct and regular contact with special advocacy groups who had their lists of demands they had to do.”

Sessions has declined to be interviewed for stories about issues that could come up at his confirmation hearing, which is scheduled for Tuesday and Wednesday.

Ellen Nakashima contributed to this report.

Correction: An earlier version of this report misspelled the name of Armand DeKeyser, Sen. Jeff Sessions’s former chief of staff.