Senior policy adviser Stephen Miller, with White House chief of staff Reince Priebus in the foreground, has been at President Trump’s side for more than a year. (Jabin Botsford/The Washington Post)

As a young conservative in liberal Santa Monica, Calif., Stephen Miller clashed frequently with his high school, often calling in to a national radio show to lambaste administrators for promoting multiculturalism, allowing Spanish-language morning announcements and failing to require recitation of the Pledge of Allegiance.

Miller’s outrage did not appear to subside after he graduated. As a Duke University sophomore, Miller penned a column, titled “Santa Monica High’s Multicultural Fistfights,” in which he ripped his alma mater as a “center for political indoctrination.”

“The social experiment that Santa Monica High School has become is yet one more example of the dismal failure of leftism and the delusions and paranoia of its architects,” Miller wrote in the 2005 article for the conservative magazine FrontPage.

In the years before he became a top adviser to President Trump and a leading West Wing advocate for the executive order temporarily halting entry into the United States from seven majority-Muslim countries, Miller was developing his skills as a culture warrior and conservative provocateur eager to condemn liberal orthodoxy — particularly on matters of race and identity. Like Trump, Miller forged that identity while immersed in liberal communities, giving him cachet with fellow conservatives for waging his battles on opposition turf.

Starting as a teenager, with his frequent calls to the nationally syndicated “Larry Elder Show,” Miller made a name for himself in conservative media circles for his willingness to take controversial stands and act as a champion for those on the right who felt maligned by a culture of political correctness.

(Bastien Inzaurralde/The Washington Post)

He produced a canon of searing columns on race, gender and other hot-button issues and, at Duke, became known to Fox News viewers as a leading defender of the white lacrosse players wrongfully accused of raping a black stripper. By his late 20s, Miller was a key aide to then-Sen. Jeff Sessions (R-Ala.), helping to torpedo a long-sought goal of immigrant advocacy groups to put millions of unauthorized Hispanic immigrants on a path to citizenship.

Today, at 31, he has emerged alongside former Breitbart News chief Stephen K. Bannon as a chief engineer of Trump’s populist “America first” agenda that has roiled the Washington debate over immigration and trade and sparked alarm among traditional U.S. allies abroad.

Miller, whose White House title is senior adviser to the president for policy, has been at Trump’s side for more than a year, joining his campaign in January 2016 when Sessions, who was sworn in Thursday as attorney general, was one of the only Republican officials to endorse the businessman’s candidacy.

While Trump at times revamped his campaign leadership, with Bannon joining relatively late in August 2016, Miller remained a steady presence whose profile and influence grew over time.

He wrote some of Trump’s most strident speeches during the campaign, including his Republican National Convention acceptance address in which Trump declared that “nobody knows the system better than me, which is why I alone can fix it.”

And Miller sometimes served as the warm-up act for Trump at his large campaign rallies, including a rip-roaring speech in Wisconsin during the Republican primary when Miller thrashed Trump’s chief rival, Sen. Ted Cruz (R-Tex.), for supporting increases in legal immigration that would result in more Muslims entering the country — a position Miller charged that Cruz held with “no regard, no concern” for how it would “affect the security of you and your family.”

After reports of Miller’s central role crafting the order imposing a 90-day ban on citizens of Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen from entering the United States, the young aide has drawn uncomfortable new scrutiny. MSNBC’s Joe Scarborough, host of the “Morning Joe” program that is a Trump favorite, recently blasted Miller as a “very young person in the White House on a power trip thinking that you can just write executive orders and tell all of your Cabinet agencies to go to hell.”

View Graphic Who is affected by Trump’s travel ban

For Miller, though, working in the Trump White House is a natural culmination of his young career — a chance to work for a president who appears to share his zeal for getting under the skin of political opponents.

“The way that people on the left abuse and slam people on the right — that’s probably the thing that’s most concerned Stephen,” said Elder, the Los Angeles-based conservative talk-show host who Miller describes as a mentor. “The lack of fairness. The left wing dominance in academia. The left wing dominance in the media. The left wing dominance in Hollywood.”

Miller’s ideological awakening found its roots in a left-leaning high school where he has written that social life and academics were badly segregated, despite what he saw as a devotion among teachers and administrators to multiculturalism.

“My best judgment at the time was that the educational answer that had been provided, which was to reject the melting-pot formula in favor of an educational formula that focused on all the things that made us different, was not working,” he told The Washington Post in an interview.

Miller said he rejects the “provocateur” label, saying it suggests that his intentions are to seek attention rather than what he says is his true goal — “to battle against slim odds, a stacked deck and powerful entrenched forces, in pursuit of justice.”

Miller said he turned away from the more liberal politics of his parents as he grew up in Santa Monica after buying a subscription to Guns & Ammo magazine and becoming familiar with the writings of actor Charlton Heston, a longtime president of the National Rifle Association.

Miller began appearing on Elder’s show, a local broadcast that is aired in 300 markets, after the 9/11 attacks, when he felt his home town lacked sufficient patriotism.

Elder said that Miller called in the first time to voice objections to his school’s failure to recite the Pledge of Allegiance daily as required by state law.

In writings at the time and later, Miller said he lobbied for the pledge recitation against a recalcitrant administration that refused to put the practice in place even after he had flagged the legal violation. “Osama Bin Laden would feel very welcome at Santa Monica High School,” he wrote in a letter to the editor at the time.

“It’s difficult to overstate the extent to which the instructional environment on campus was breathtakingly PC,” Miller said in an interview.

Mark Kelly, who was the principal at the time, said he did not recall the episode as a major fight. When Miller flagged the issue, Kelly said he researched the law and realized that the school, indeed, needed to change its policy and institute the recitation of the pledge. Miller was invited to lead the pledge after it was reinstated.

“Stephen was right,” Kelly recalled.

The victory was a validation for Miller of the necessity to fight powerful figures who opposed his views.

Miller pushed the school administration over his desire to host an on-campus speech by David Horowitz — a onetime Marxist, then controversial far-right conservative — who became an early mentor and would later introduce Miller to Sessions.

Horowitz recalls being immediately impressed with Miller. “One of the things that struck me when I became a conservative was that conservatives don’t have any fight,” Horowitz said. “They don’t have any stomach for it. . . . Stephen Miller had that from the get-go.”

Cultural-identity issues appeared to particularly animate Miller. In a column in his high school newspaper, titled “A Time to Kill,” he urged violent response to radical Islamists.

“We have all heard about how peaceful and benign the Islamic religion is, but no matter how many times you say that, it cannot change the fact that millions of radical Muslims would celebrate your death for the simple reason that you are Christian, Jewish or American,” Miller wrote.

Ari Rosmarin, a civil rights lawyer who edited the student newspaper at time, recalled that Miller was especially critical of a Mexican American student group.

“I think he’s got a very sharp understanding of what words and issues will poke and provoke progressives, because he came up around it and really cut his teeth picking these fights that had low stakes but high offense,” Rosmarin said.

That skill led Miller to become a mini-celebrity in conservative intellectual circles because of his passion, age and home town. He appeared 70 times on Elder’s show before his high school graduation, according to the host.

“He found a really unique role to play that was deeply attractive to national conservatives,” Rosmarin said. “He was like a lonely warrior behind enemy lines.”

In the halls of Santa Monica High School, though, where students and teachers took pride in their ethnic diversity and liberal values, Miller was becoming something of a pariah. That environment prompted Miller to become even more assertive, recalled one of his former teachers.

“He had to come on a little strong as a defense mechanism — just to survive,” said the teacher, who spoke on the condition of anonymity out of fear for how colleagues would react to the defense of an alumnus so closely associated with Trump. “He came under a lot of fire, even from teachers.”

At Duke, Miller wrote a biweekly column for the student newspaper that regularly aroused the ire of classmates.

“Men and women are in many ways the same, but they’re also innately and magnificently different,” he wrote in one column that argued laws requiring men and women to be paid equally would hurt businesses and that the pay gap largely resulted from women taking time off for childbirth, being less willing to ask for raises and being less likely to take part in hazardous work.

“The point is that the pay gap has virtually nothing to do with gender discrimination,” he wrote. “Sorry, feminists. Hate to break this good news to you.”

In a column titled “The Case for Christmas,” Miller, who is Jewish, argued that the holiday should be more widely recognized as a “crucial American holiday.”

“Christianity is embedded in the very soul of our nation,” he wrote.

Miller stepped into the national spotlight after three white lacrosse players were falsely accused of rape in a case rife with racial tension. The players were eventually cleared and the local district attorney was disbarred for prosecutorial misconduct in the case. Miller wrote a series of columns about the case and appeared on national television to discuss it.

“This travesty has been allowed to continue because we live in a nation paralyzed by racial paranoia,” he wrote in November 2006, writing that professors and others were frightened to speak in defense of the students because the district attorney had turned the case into a racial crusade and opposition “would be perceived negatively by the black community and that there would be a political price to pay.”

Speaking years later about his role as an advocate for the players, Miller told The Post: “The one takeaway I have from it is that in a difficult moment, I took a stand on principle — and I was correct.”

Reflecting more broadly on his college-era columns, Miller said his writings were a good reflection of his views at the time. But, he said, “I would surely hope that any person who was a writer about political and controversial topics in college would find that their thoughts had matured on a variety of issues.” He declined to outline where his own views had changed over time.

Miller’s outspokenness in the lacrosse case first brought him to the attention of Richard Spencer, a white nationalist who was a Duke graduate student at the time. Spencer said he became friendly with Miller through the Duke Conservative Union in fall 2006.

“He was very out in front, very bold and strong,” Spencer said in an interview.

Spencer last year told the Daily Beast that he was a “mentor” to Miller, which Miller has angrily denied.

“I condemn him. I condemn his views. I have no relationship with him. He was not my friend,” Miller said.

Miller noted that he served on campus as the executive director of the leading conservative group, which put him in contact with Spencer. “Our interaction was limited to the activities of the organization, of which he was a member, and thus ceased upon graduation,” Miller said.

But Spencer said that the two met frequently during their Duke days. As first reported by Mother Jones magazine, they both helped organize an immigration debate between Peter Brimelow, an anti-immigration activist whose website has been labeled a hate site by the Southern Poverty Law Center, and Peter Laufer, who advocated for opening the southern U.S. border. Spencer praised Miller’s media savvy and organizational skills in advance of that event.

David Bitner, a friend of Miller’s who also belonged to the conservative club at Duke, said the two did interact in the small group. But Bitner called it “scurrilous libel” for Spencer to claim he was Miller’s mentor.

“Richard Spencer believes in white identity politics. Stephen Miller disavows identity politics,” he said.

Nevertheless, Miller’s role in the White House has been greeted with enthusiasm by Spencer and other white nationalist figures.

“He is not a white nationalist,” Spencer said. “But you can’t be this passionate about the immigration issue and not have a sense of the American nation as it historically emerged.”

After attending Trump’s inauguration, Jared Taylor, another high-profile white nationalist, posted a piece to his website in which he wrote that Trump is “not a racially conscious white man” but that there “are men close to him — Steve Bannon, Jeff Sessions, Stephen Miller — who may have a clearer understanding of race, and their influence could grow.”

In an interview, Taylor said he was “speculating” and that he has not met or spoken with Miller.

Miller said he has “profound objections” to the views advanced by Taylor and Spencer, saying: “I condemn this rancid ideology.”

Elder, who is black, said he has never heard Miller speak of Spencer or Taylor or express what he considers racist views.

Instead, Elder said, Miller believes as he does: “Race and racism are no longer major problems in America. This is the fairest majority-white country in the world. If you work hard and make good decisions, you’ll be fine.”

Miller said that his views at the time were best summed up in a 2005 column in the Santa Monica Mirror, titled “My Dream for the End of Racism,” in which he argued that Americans should focus on how far the country has come in overcoming such prejudice. “No one claims that racism is extinct — but it is endangered,” he wrote. “And if we are to entirely extract this venom of prejudice from the United States, I proclaim Americanism to be the key.”

Focusing on “multiculturalism,” he wrote, has had the effect of keeping different groups separate.

Miller’s White House role is in many ways a departure for an activist who has mostly seen himself as representing an oppressed political minority. Now he holds the power, helping to drive the government while working steps from the Oval Office.

Bitner said he wonders how Miller’s tactics will translate.

“I don’t think he’s had the opportunity to practice this,” he said. “These are all outsiders, many of them people who have been vocal minorities. How do you transition from there to governing?”

Alice Crites contributed to this report.