By SHARON LaFRANIERE and MATT APUZZO
The New York Times

During nearly two decades in the Senate, Jeff Sessions had never endorsed anyone in a presidential primary. But last January, the Alabama Republican, afraid that his party was floundering, sent a five-point questionnaire to all its presidential contenders to determine who might deserve his support.

Just one answered: Donald J. Trump.

Mr. Sessions is in many ways Mr. Trump’s antithesis: reedy-voiced, diminutive and mild-mannered, a devout Methodist and an Eagle Scout who will soon celebrate a golden wedding anniversary with his college sweetheart. His father ran a country store in the Deep South. And he is widely regarded as rigidly honest and inflexible on issues he considers matters of principle. Mr. Trump has meandered across the political spectrum; Mr. Sessions has been a deeply conservative Republican his entire life.

But besides their age — both are 70 — Mr. Sessions shared one trait with Mr. Trump: He was an outsider, dismissed by much of the Republican Party as a fringe player on all but his signature issue, immigration. The two men unexpectedly bonded over their willingness to buck the establishment and the unlikely hope that lower-middle- and working-class voters would carry a billionaire to the White House.

For Mr. Sessions, that alliance has paid off in a fashion that few ever imagined. Rejected for a federal judgeship, passed over for a crucial Senate committee chairmanship and long considered too far right to attain a cabinet post, he has defied the odds.

Within days, he could be confirmed as attorney general of the United States.

Some cabinet nominees arrive at confirmation hearings with records that require considerable guesswork. Not Mr. Sessions. His rock-ribbed conservatism was forged in the deep poverty and isolation of rural Alabama, sharpened during 16 years as a federal prosecutor and state attorney general and polished as a senator. After one of the most liberal periods in Justice Department history, Mr. Sessions is expected to execute an about-face on the Obama administration’s policies of immigration, criminal justice and — many critics fear — civil rights.

He argues that immigrants are siphoning billions in welfare payments, committing crimes and snatching jobs from Americans. He has questioned whether the Constitution guarantees citizenship to anyone born in the United States, as the 14th Amendment states, and has insisted that the First Amendment doctrine of separation of church and state has been too broadly interpreted. He declared same-sex marriage an indisputable threat to American culture and once went to court to deny funding for gay student groups. Overreaching by the Justice Department’s Civil Rights Division, he has said, at times has led to “civil wrongs.”

He favors stiff, mandatory penalties for drug offenses, believes that the government has grown soft on crime and objects to what he sees as unwarranted criticism of police behavior.

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Mr. Sessions is not a uniquely conservative pick; John Ashcroft, attorney general under President George W. Bush, held similarly strident views. But Mr. Ashcroft was a party stalwart whom any number of Republican presidents might have nominated. Mr. Sessions offers an uncompromising brand of conservatism that combines Christian and small-government values with strains of populism and a willingness to say the unpopular, or even offensive. He speaks to a disenchanted electorate that includes the white, nationalistic fringes of his party. In short, he is a uniquely Trump nominee to lead the Justice Department.

To many Trump supporters, he is a rare public servant with the backbone to enforce the nation’s laws strictly, regardless of political consequences. “He has been the leader of this populist revolt against the political elite,” Stephen K. Bannon, the former head of Breitbart News Network who will be a senior White House adviser, said in February.

Critics see Mr. Sessions as a throwback to a bygone South. “His whole life, he has been on the wrong side of every issue,” said Wayne Flynt, a politically progressive Alabama history professor who has followed his career for decades. On questions about voting, gays and immigration, he said, “he has argued to narrow democracy, not broaden it.”

The roots of his ideology, and the combination of independence and tenacity that has carried Mr. Sessions to this point, can be found in rural Alabama, where he grew up.

A Strict Code

Jefferson Beauregard Sessions III was named after his father, who was named after his grandfather, who was named after the Confederate president Jefferson Davis, his parents once said. Buddy, as he was called, grew up an only child on the ragged edge of Alabama’s famous Black Belt in Hybart, a one-crossing hamlet where his father ran a store. The family lived in a one-story house with no driveway, a small concrete front stoop and a heating system consisting of a fireplace and space heaters.

Birmingham had a steel industry. Mobile had a port. But around Hybart, work was limited mostly to logging or farming. Neighboring Wilcox County, home to the nearest town of any size and Mr. Sessions’s high school, then was one of the nation’s poorest. It still is.

A 1969 yearbook photo of Mr. Sessions as a student at Huntingdon College in Montgomery. He led the student government association and the Young Republicans club there.

He learned thriftiness from his parents, who grew up during the Depression. Upon becoming a United States attorney in 1981, he had only $750 in the bank, records show. Friends joke that even after he attained the comfortable life of a senator decades later, he refused to replace an aging car or the outdated kitchen countertops at his home in Mobile.

It was an environment that fostered Mr. Sessions’s belief in frugality and self-reliance, bounded by a strict — if much disputed — code of what was and was not fair.

It also bred, even early on, a skeptic’s eye toward elites. His parents were longtime Republicans in a state that had been run by Democrats since Reconstruction. In high school, as racial politics laid the foundation for the eventual Republican takeover of the South, Mr. Sessions was fascinated by Phyllis Schlafly’s book “A Choice Not an Echo,” a catechism on the split between the Republican Party establishment and its right wing. The book enjoined true conservatives to topple the party’s kingmakers and compromisers, presaging the rise of the Tea Party and Mr. Trump — and now, Mr. Sessions himself.

Unpopular ideas did not faze him, even as a schoolboy. His mother told one reporter, “That boy could argue with a signpost.” His high school yearbook photo bore the caption: “He is a host of debaters in himself.”

Alabama’s economic struggles helped define his political priorities. As a young man, he watched timber imports eat into local logging jobs, cheaper foreign steel hasten the closing of Birmingham mills, and immigrants take jobs in the fields and chicken processing plants. Most economists say those changes were largely unavoidable as the United States shifted from an economy based on manual labor to one rooted in services and knowledge. But Mr. Sessions saw a threat to the hard-working families he had grown up with, former aides said.

To Alabama voters, weary of decades of Democratic back-scratching and scandals, Mr. Sessions seemed a breath of fresh air when he emerged on the political scene in 1994, after 12 years as the top federal prosecutor in Mobile. As the state’s attorney general, his first elective post, he slashed staff, pay, travel, cars and supplies. Republican leaders hoped he would come to the rescue of the former governor, Guy Hunt, who was removed from office after a 1993 ethics conviction. Instead, Mr. Sessions asked a federal appeals court to uphold the conviction.

The business-dominated establishment wing of Alabama’s Republican Party is closer to the state’s senior senator, Richard C. Shelby. Mr. Sessions’s political base included rural and suburban working-class and evangelical white voters — the same constituencies that proved crucial to Mr. Trump’s success in November. “Sessions had a Trump movement before there was a Trump,” Professor Flynt, of Auburn University, said.

His record as Alabama’s attorney general — he served just two years before winning election to the Senate in 1996 — showcases his fiercely conservative views. Mr. Sessions supported reviving chain gangs of volunteer inmates. He defeated a court order that would have directed more state money to schools in poor districts by arguing that a single judge had usurped management of the entire state school system. He supported efforts to tighten identification requirements for Alabama voters and backed a county judge who posted the Ten Commandments in his courtroom and opened court with a daily prayer.

Mr. Sessions’s nomination to a federal judgeship in 1986 foundered when senators of both parties questioned his commitment to civil rights. CreditTerry Ashe/The LIFE Images Collection, via Getty Images

Alabama liked what it saw: Seeking his fourth term in 2014, Mr. Sessions was the only United States senator to run unopposed. “He doesn’t hide who he is. He’s a conservative guy,” said former Senator Mark Pryor, a Democrat from Arkansas who once led the Senate’s weekly prayer breakfast with Mr. Sessions. “He doesn’t represent Massachusetts. He represents Alabama.”

But his rigid views and his willingness to buck the Republican leadership isolated him in the Senate. A fervent budget hawk, he was ready with his own spending plan when Republicans captured the Senate after the 2014 elections. But party leaders passed him over for chairmanship of the powerful Budget Committee, leaving him the longest-serving senator without a committee to lead. Former aides describe the decision as payback for Mr. Sessions’s relentless opposition to bipartisan efforts to ease immigration restrictions.

Republican purists like the radio host Rush Limbaugh said Senate power brokers were punishing a courageous truthsayer. “That alone tells you where the Republican leadership mind-set is on this,” Mr. Limbaugh said on his program in 2014. “They want to take out the one primary voice of opposition.”

Civil Rights

There is perhaps only one area in which Mr. Sessions’s views are in question. It is the source of his sole setback in four decades of public life and most of the controversy over his nomination.

As Mr. Sessions attended his church youth group and worked toward the rank of Eagle Scout in the early 1960s, Alabama was emerging as ground zero of the civil rights movement, the backdrop for violence and bravery since immortalized in museums. But as he has himself suggested, the era’s historic tumult largely escaped him.

Segregation permeated the rural Alabama of his youth. As late as 1985, his father told a local paper that he believed in it, although he stressed he was not speaking for his son. Wilcox County High School, where Jeff Sessions was voted senior class president in 1964, was an all-white institution. African-Americans, the majority of county residents, were largely illiterate, living in unpainted wooden shacks insulated with newspapers, their children shunted to squalid schools with no instructional materials.

In March of Mr. Sessions’s senior year, demonstrators from the Student Nonviolent Coordinating Committee and the Southern Christian Leadership Conference came to town, demanding that African-Americans be allowed to register to vote. Police officers responded with tear gas and smoke bombs. The same month, state troopers armed with billy clubs attacked African-Americans as they began a historic march in Selma, 35 miles north of Wilcox County High.

A few months later, the Voting Rights Act of 1965 opened the polls to African-Americans. The year after Mr. Sessions graduated, the Justice Department pried open the doors of Wilcox County schools for African-American students, winning a court judgment against a school board that had flatly declared that “desegregation is not good for education.”

By then, Mr. Sessions was a history major at Huntingdon College, a small, all-white Methodist school in Montgomery. He led the Young Republicans club — maybe a dozen students, including Mary Blackshear, whom he met on a hayride and married soon after graduation. “Even though we were in Montgomery at a time when so much was going on, it was like we were in a little bubble or something,” said Phebe Lee, a college friend and club member.

Mr. Sessions acknowledged as much in February, at a congressional ceremony honoring the Selma marchers. “As a child and a teenager, I saw evidence of discrimination every day,” he said. “Certainly, I feel I should have stepped forward more.”

Mr. Sessions co-sponsored legislation awarding Alabama’s civil rights marchers and Rosa Parks Congressional Gold Medals, but he has expressed mixed views about the Justice Department’s enforcement of civil rights. In the mid-1980s, he called the Voting Rights Act, which prohibited racial discrimination at the polls, “an intrusive piece of legislation” and said that federal judges of that era “can be criticized legally for exceeding jurisdiction.”

On balance, he said, the law was necessary, and he voted with every other member of the Senate in 2006 to extend its provisions for another 25 years. But in 2013, after the Supreme Court invalidated one of the act’s core provisions that required Justice Department approval to change election laws in places with histories of discrimination, he called it “good news, I think, for the South.”

Mr. Sessions has long accused the department of overstepping its authority by promoting minority rights that conservatives argue have no clear basis in law. “There is a perception, not altogether unjustified, that this department’s Civil Rights Division goes beyond fair and balanced treatment, but has an agenda,” Mr. Sessions said last year. “That’s been a troubling issue for a number of years, frankly.”

Critics fear such comments presage a rollback in civil rights enforcement. “Jeff Sessions is emblematic of too many white Southerners who learned very little from the civil rights movement, except how to be more creative in carrying out an anti-civil-rights agenda,” said Allen Tullos, a history professor at Emory University.

Under President Obama, the Justice Department has threatened civil rights lawsuits to force police departments to change policies on the use of force, advocated gay rights and told local school districts to let transgender students use bathrooms that match their gender identity.

Advocates and career prosecutors see a shift in the department’s work on gay, lesbian and transgender issues as all but certain under Mr. Sessions. As Alabama’s attorney general in the mid-1990s, he defended a state law barring funding for gay student groups on state college campuses, arguing that their very existence encouraged violation of state sodomy laws. A federal appeals court disagreed, striking down the law as “blatant” discrimination. In the Senate, he voted against making it a federal hate crime to attack people based on their sexual orientation.

Mr. Sessions has also questioned the use of consent decrees — one of the Justice Department’s most powerful civil rights tools — as “an end run around the democratic process” and a dangerous exercise of raw government power. The Obama administration has relied on consent decrees, in which local governments agree to make new policies to avoid battling the federal government in court, to transform police training, improve conditions in prisons and change how officers make arrests and use force.

“I think you’ll see the Civil Rights Division go back to its more traditional role in terms of law enforcement,” said Larry Thompson, a former deputy attorney general and longtime friend of Mr. Sessions. “I don’t think he’s going to countenance a police officer shooting someone under color of law, but more than the current administration, he’ll make sure to stand up for law-abiding citizens when one of these unfortunate situations occur.”

Mr. Sessions’s last nomination to a federal post, a federal judgeship in 1986, foundered over questions by senators of both parties about his commitment to civil rights. Accounts of the nomination battle typically focus on testimony about a string of racially insensitive comments he was accused of making as a federal prosecutor. Those included statements — which he said were taken out of context but did not deny — that the N.A.A.C.P. and the American Civil Liberties Union were “un-American” groups that “do more harm than good.”

But perhaps most crucial to his rejection was his 1985 prosecution of three longtime black community activists on ballot-fixing charges. One was Albert Turner, an adviser to the Rev. Dr. Martin Luther King Jr. and one of the Selma marchers attacked by state troopers.

In 1984, Mr. Turner, his wife, Evelyn, and Spencer Hogue Jr. were working to elect a black candidate for local office over another African-American who, they believed, was in league with white politicians. A federal grand jury convened by Mr. Sessions’s office charged them with 29 criminal counts for allegedly altering about two dozen absentee ballots without the voters’ consent.

Albert Turner, left, with his wife, Evelyn, and Spencer Hogue Jr., and a redistricting map of Perry County, Ala. In 1984, a federal grand jury convened by Mr. Sessions’s office charged each of them with 29 criminal counts for allegedly altering about two dozen absentee ballots without the voters’ consent. They were acquitted.

The case became a cause célèbre among local African-Americans and among civil rights lawyers, who saw it as part of a broader effort by the Reagan administration’s Justice Department to intimidate black voters. At trial, the case collapsed; most voters testified that the defendants were trying to help them complete ballots, not fix them. A jury swiftly acquitted them.

Among other concerns, Senator Howell Heflin, an Alabama Democrat who sat on the Senate Judiciary Committee at the time, doubted that the case merited the full force of the federal government, Steve Raby, Mr. Heflin’s former chief of staff, said in an interview. Losing the support of a home-state senator proved fatal. It was only the second time in 48 years that a judicial nomination died in committee.

Mr. Sessions, who prides himself on methodical preparation, has said he was “a babe in the woods” before the committee. If so, he has learned his lesson: In recent weeks, a string of African-Americans, whom he has recruited, hired and promoted, have come forward to testify to his lack of racial animus.

Mr. Sessions is also mounting a vigorous effort to show that he stood up for civil rights as a federal prosecutor. He cites his successful pursuit of two Ku Klux Klan members who in 1981 brutally murdered a black teenager. “There were a lot of Southern United States attorneys who were not very welcoming to attorneys from the Civil Rights Division in the 1980s,” said Barry Kowalski, the Justice Department attorney on the case and a lifelong Democrat. “And he was.”

Mr. Sessions has also revised a list of the 10 most important cases that he “personally handled” as a prosecutor to include four voting rights and school desegregation cases, even though his involvement was minimal, former Justice Department lawyers said.

Mr. Sessions has stood behind the Perry County prosecution. And he still considers voter fraud a problem, though studies have consistently shownthat it is extraordinarily rare.

Albert Turner died in 2000. His son and namesake, who is a Perry County commissioner, now defends Mr. Sessions. “He is not a racist,” he said in a statement. “I believe him when he says he was simply doing his job.”

His mother, Evelyn Turner, 80, does not. In February, at the congressional ceremony that honored her husband and other Selma marchers, the senator tried to hug her, she said. “But I said, ‘No, get off of me,’” she said. “I know he has not changed.”

Crime and Punishment

After he was elected senator, taking a seat on the same Judiciary Committee that denied him the judgeship, Mr. Sessions seemed to bear no grudge against those who had humiliated him in 1986. He collaborated with Senator Edward M. Kennedy of Massachusetts on a bill to reduce prison rape. He also worked with Democrats to correct sentencing disparities that resulted in harsher penalties for those convicted of crimes involving crack cocaine, who were predominately black, than those convicted of powder cocaine, who were more likely to be white.

But in general, he was viewed in the Senate as a bill killer, not a bill sponsor.

 Mr. Sessions at the Capitol in June 2013. A frequent topic he would raise on the Senate floor was what he saw as the Obama administration’s leniency toward drug offenders. CreditDrew Angerer for The New York Times

“Preventing something bad from happening is just as important to him as getting something good done,” said Marcus Peacock, a former senior aide.

C-Span played endlessly in his office and, if something disagreeable caught his ear, he summoned staff members to help him craft an immediate response in pencil on a yellow legal pad. “Even if you had meetings, the assumption is you’d be there,” Mr. Peacock said. Then the senator was off to the Senate floor, often to speak to an empty room.

A frequent topic was what he saw as the Obama administration’s leniency toward drug offenders. Mr. Sessions served as a federal prosecutor in Mobile in the heyday of the nation’s war on drugs, a time when Congress passed lengthy mandatory minimum sentences for drug crimes and the prison population ballooned. He has proudly described himself as a lieutenant in the nation’s drug war.

Many politicians now regard that as a period of excessive punishments. The Obama administration — using clemency, discretion and more lenient sentencing laws — has undone many of that era’s policies and helped reduce the federal prison population for the first time in decades.

But Mr. Sessions believes those long prison sentences produced low crime rates. “It’s mathematics,” he has said: the more criminals in prison, the fewer on the street. When Mr. Obama likened marijuana to alcohol, Mr. Sessions was “heartbroken.” “This drug is dangerous,” he said last year, adding, “Good people don’t smoke marijuana.”

Liberals may chafe at such rigidity, but Mr. Sessions shares their disdain for the philosophy of “too big to jail” — the notion that prosecutors should consider whether bringing charges against large companies would imperil the economy. “This is a dangerous philosophy,” he said in 2010 amid Justice Department investigations into the banks at the heart of the financial meltdown. “Normally, I was taught, if they violated the law, you charge them. If they did not violate the law, you do not charge them.”

A Defining Issue

But no single topic energizes Mr. Sessions more than immigration. In 2013, when the Senate was considering a pathway to citizenship for immigrants, Mr. Sessions spent more time on the Senate floor than its top leaders, aides said. The issue has defined his Senate career and, along with trade, formed his link to Mr. Trump.

Soon after his arrival in Washington, Mr. Sessions had received a visit from Roy Beck, an author who had recently formed the group NumbersUSA to advocate reduced immigration. Mr. Beck arrived at Mr. Sessions’s fourth-floor Senate office building prepared to make a sales pitch.

Immigrants, here legally or illegally, he said, were taking jobs from American workers. Democrats, because of their Hispanic constituencies, were reluctant to address this, he said. And Republicans were too aligned with big corporations that benefited from immigrant labor. Mr. Beck figured that, as a former prosecutor, Mr. Sessions might be sympathetic at least to the idea that America’s immigration laws should be better enforced.

 Mr. Sessions in December 2014, appearing with law enforcement officials from around the country to criticize President Obama’s immigration policies. The issue of immigration has defined his Senate career.CreditStephen Crowley/The New York Times

Almost immediately, Mr. Sessions began finishing Mr. Beck’s sentences. He noted with dismay the transformation of Alabama’s poultry industry, which for years had provided jobs — grueling, punishing work, but jobs nonetheless — to even the poorest, least-educated workers. “He saw a work force that was maybe half white, half black become mostly foreign,” Mr. Beck recalled.

“This is what justice is about,” Mr. Sessions told him. “You don’t put your finger on the scale against the poor person who’s trying to make a living.”

Since then, Mr. Sessions has become the most reliable congressional ally of anti-immigration groups.

He supported a state law in Alabama that, among other things, required public schools to verify the immigration status of students and their parents and made it a crime for immigrants to not carry their legal papers. The goal was to make every aspect of life for illegal immigrants so unbearable that they would deport themselves. Federal courts ultimately gutted the law.

Mr. Sessions’s views have made him a target of critics who say he works too closely with people who have racist, xenophobic views. Several of the groups he has worked alongside were founded or nurtured by the activist John Tanton, who has described the anti-immigration fight in racial terms. “For European-American society and culture to persist requires a European-American majority,” Mr. Tanton once warned a friend.

In 2015, Mr. Sessions received the annual Keeper of the Flame award from the Center for Security Policy, a Washington think tank that promotes anti-Muslim conspiracy theories. Its founder, Frank Gaffney, has argued, among other things, that Mr. Obama is secretly a Muslim and that the crescent in the new logo of the Missile Defense Agency is a veiled sign that the United States has submitted to Islamic law.

Mr. Sessions has for years heard claims that his views are rooted in a fear of foreigners. He has steadfastly denied it. “It is not xenophobic but our patriotic duty to defend the integrity of our borders and the rule of law,” he said in 2014.

When business leaders said more foreign workers would help the economy, Mr. Sessions mocked them for playing “masters of the universe” from behind the high fences of their estates. His office was a font of research that he sometimes personally thrust into the hands of fellow senators.

The U.S. Chamber of Commerce, a traditional base of Republican support, strongly supported immigration legislation and went so far as to say that Republicans should not bother running a presidential candidate in 2016 if they did not pass it. “Gosh,” Mr. Beck said to Mr. Sessions. “How far can you go on this?”

“How many votes does the Chamber of Commerce have?” Mr. Sessions quipped.

When it became clear that, over his vehement objections, the Senate would pass an immigration bill in 2013, Mr. Sessions helped rally conservative House members to defeat the bill and make sure it would not become law.

As attorney general, Mr. Sessions would oversee the hiring of immigration judges and the operation of immigration courts. Though the Department of Homeland Security directly enforces immigration laws, the Justice Department is involved in helping set immigration legal policy and in prosecuting people who return to the country after being deported.

“Throughout the debate on comprehensive immigration reform, no one was more anti-immigrant than Jeff Sessions,” said Senator Chuck Schumer of New York, the Democratic leader. “And for me that outweighs the fact that he is a colleague and someone that I have worked with well on other issues like trade.”

The Trump Campaign

For years, Mr. Sessions envisioned a day when the Republican Party would shed its big-business, country-club image and become a workers’ party. But his arguments gained little traction. In 2012, he believed, Mitt Romney handed Mr. Obama a second term by failing to appeal to voters earning less than $50,000. By 2015, Mr. Sessions was disillusioned and saw his party in disarray.

In a 23-page memo to his colleagues that January, Mr. Sessions said the road to capturing working-class voters was clear: The party, he wrote, had to show how lax immigration policies had stolen their jobs and erased their prospects for moving up the social ladder. “Republicans cannot win in 2016 without these voters,” he wrote, “and Republicans cannot win these voters unless they prove that they are willing to break from the donor class.”

When Mr. Trump announced his presidential bid six months later, Mr. Sessions saw a potential political mold-breaker. Within weeks of Mr. Trump’s campaign announcement, the two men talked by telephone about trade and immigration.

In a 90-minute meeting in the senator’s office in September 2015, Mr. Trump assured Mr. Sessions that he was in the race to win. The senator’s staff shared position papers and a top aide, Stephen Miller, joined the campaign.

When Mr. Sessions sent Republican candidates his questionnaire, every candidate except Mr. Trump ignored it.

“It wasn’t easy” to gain Mr. Sessions’s support, Mr. Trump said after winning his endorsement late last February, just before sweeping a string of Southern primaries. “I put in a lot of work on the subject matter.”

Nor was it easy for the senator. Longtime Republican allies called to express their fury. Others refused to take calls from his staff. An article in the conservative National Review branded him “a prostitute.”

 The Republican National Convention in July of last year. Mr. Sessions had the idea of inviting people whose relatives were murdered by illegal immigrants, according to Rudolph W. Giuliani, who credits the senator with shaping Mr. Trump’s immigration views. CreditAlex Wong/Getty Images

But Mr. Sessions did not waver, even at the lowest points of Mr. Trump’s campaign. When Mr. Trump was denounced for his anti-immigration rhetoric, colleagues said, Mr. Sessions offered reassurance. He helped craft a crucial immigration speech and prepare for the presidential debates. It was the senator’s idea to bring to the Republican convention people whose family members had been murdered by illegal immigrants, according to Rudolph W. Giuliani, a campaign adviser who credits Mr. Sessions with shaping Mr. Trump’s immigration views.

A Crucial Test

For all that is known about Mr. Sessions, one thing that is unclear is how he will measure up to what he has declared to be a crucial test of an attorney general’s qualifications: the willingness to stand up to the president, who in this case plucked him from obscurity.

Critics point to his support for President George W. Bush’s warrantless wiretapping program and Justice Department memos authorizing waterboarding as signs that Mr. Sessions takes a broad view of presidential power.

But his supporters point to a track record of insisting on Justice Department oversight and independence. Mr. Sessions chastised the Obama administration for refusing to defend the Defense of Marriage Act, saying that senior Justice Department lawyers should have told the president that they insisted on doing so, as a matter of principle. Mr. Sessions also did not support Attorney General Loretta E. Lynch’s nomination because she stood behind Mr. Obama’s authority to enact immigration policy through executive orders, which he called an abuse of presidential authority.

The Justice Department can help the president achieve policy goals, he said, but must stand firm against overreaching.

“You’ve got to be prepared to say no,” he said in 2011. “And if you do, politicians normally come around. You don’t have to do it publicly. You just tell him, ‘Mr. President, you cannot do that.’”

Now, as Mr. Trump embarks on a presidency in which he promises to remake Washington and dispense with many of its traditions, it will fall to Mr. Sessions to decide if and when to say no. And his reputation for standing up to the powers that be, consequences be damned, may face its stiffest test yet.