“He just seemed really happy,” said Charles Gould, a classmate and friend at the time, “as if that’s how he planned it.”
In the years since, Mr. Miller has rocketed to the upper reaches of White House influence along a distinctly Trumpian arc — powered by a hyper-fluency in the politics of grievance, a gift for nationalist button-pushing after years on the Republican fringe and a long history of being underestimated by liberal forces who dismissed him as a sideshow since his youth.
Across his sun-kissed former home, the so-called People’s Republic of Santa Monica, they have come to regret this initial assessment. To the consternation of many former classmates and a bipartisan coalition of Washington lawmakers, Mr. Miller has become one of the nation’s most powerful shapers of domestic and even foreign policy.
“The 31-year-old?” Senator John McCain, Republican of Arizona, muttered to reporters earlier this year, despairing over who might be making decisions in Mr. Trump’s White House.
Yet on perhaps the president’s signature issue — immigration policy — Mr. Miller has emerged in recent days as the driving force behind the administration’s insistence on a wish list of hard-right proposals as part of any deal with Democrats to protect young undocumented immigrants from deportation. White House demands include a crackdown on unaccompanied children at the border, the construction of a border wall with Mexico and legislation to sharply reduce legal immigration.
As the surviving watchman on the president’s right flank since the removal in August of Stephen K. Bannon as chief strategist, Mr. Miller also remains a key craftsman in speechwriting at the White House. Mr. Trump, who has long prized Mr. Miller’s fierce loyalty, has embraced his instincts to sharply restrict the number of refugees admitted to the United States next year and to impose new travel restrictions on several predominantly Muslim countries and others deemed to be national security risks.
From the administration’s opening stanzas — when Mr. Trump let fly his “American carnage” inaugural address — to his swaggering turn last month before the United Nations, it is Mr. Miller’s worldview, as often as anyone’s, that the president projects on the grandest scale.
“We have this running joke,” said Kellyanne Conway, counselor to the president, “that if we were going to get key man’s insurance on anyone, Stephen would top the list.” She was referring to policies that companies take out on their most important employee.
The Beginnings in Santa Monica
Mr. Miller’s journey to this point, outlined over dozens of interviews with friends, classmates and current and former colleagues, is a triumph of unbending convictions and at least occasional contrivance. It is a story of beliefs that congealed early in a home that he helped nudge to the right of its blue-state ZIP code, and of an ideology that became an identity for a spindly agitator at a large and racially divided public high school.
These formative years supplied the template for the life Mr. Miller has carved out for himself in Washington, where he remains the hard-line jouster many of Mr. Trump’s most zealous supporters trust most in the White House — and many former peers fear.
“I can hear Stephen’s voice,” said a fellow Santa Monica student, Nick Silverman. “Even when Trump reads these statements, I know, ‘That’s Stephen.’”
Through Mr. Miller’s nearly nine months in the Trump White House, the question — how did he come from here? — has curdled across these eight square miles of progressive oceanside paradise, where a stroll near the beach can quickly produce images that border on a self-parody of limousine liberalism. Environmentalist stickers festoon a neighborhood pocked with gas guzzlers; a small dog, seated in a stroller, twitches in the sea breeze, rumbling past a homeless man sprawled across a sidewalk bench.
“It does have this tang of the seething id of Santa Monica,” another student, Jake Zambas, said of Mr. Miller’s nativist streak, noting that their high school, like the town, was largely self-segregating. “Everyone here is just a scared white person.”
In his time on this campus of roughly 3,000 students, Mr. Miller sculpted the brand of hard-charging conservatism that would deliver him to the president’s ear, tracing a pathway at once complicated and straightforward. Mr. Miller, the middle child in a financially comfortable Jewish family, plainly relished the attention and notoriety of being the city’s red-hued exception, according to classmates — some of whom recalled chuckling at, or at least shrugging off, the antics of their resident gadfly. The line between puckishness and principle blurred in due time.
Mr. Miller set off on a patriotic semi-striptease before the editor of the student newspaper, according to the editor, Ari Rosmarin, theatrically removing a button-down to reveal an American flag T-shirt in protest of an article he found inconsistent with the national interest. (The White House denied any symbolic unbuttoning, though officials confirmed Mr. Miller’s fondness for the T-shirt.)
He jumped, uninvited, into the final stretch of a girls’ track meet, apparently intent on proving his athletic supremacy over the opposite sex. (The White House, reaching for exculpatory context, noted that this was a girls’ team from another school, not his own.)
Most memorably, classmates say, Mr. Miller established a reputation for barreling eagerly toward racial tinderboxes, leaving some to wonder whether his words were meant to be menacing or hammy. Jason Islas, who had been friendly with Mr. Miller in middle school, has little doubt.
Shortly before the start of ninth grade, Mr. Islas said, he received a call from Mr. Miller informing him that the two could no longer be friends.
“He gives me this litany of reasons,” Mr. Islas said.
Most were petty, if mean, he recalled: an insult about his social awkwardness, a dig at his acne-specked face. But one stuck out.
“He mentioned my Latino heritage as one of the reasons,” Mr. Islas said. “I remember coming away from the conversation being like, ‘O.K., that’s that.’”
Sarah Huckabee Sanders, the White House press secretary, called Mr. Islas’s account “a completely inaccurate characterization of their relationship, or lack thereof,” disputing his recollection and suggesting the two were more acquaintances than friends. (Mr. Miller declined to be interviewed for this article.)
Several students said Mr. Miller’s trail of racially tinged comments amounted to a pattern. He railed against bilingual announcements, asking in a local editorial why there were “usually very few, if any, Hispanic students in my honors classes, despite the large number of Hispanic students that attend our school.”
Latino students remembered him engaging them outside group meetings, asking why they required a separate forum to discuss issues of identity, and chafing at Spanish being spoken in the halls.
“He tended to make some of the Spanish language stuff very personal,” said Moises Castillo, a classmate who described the exchanges as hurtful to this day. “There was a ‘if you’re not speaking English, perhaps you should go somewhere else.’”
He was asked whether Mr. Miller may have been leaning into a sort of provocative shtick, or crafting a character deliberately. In the campaign speech, after all — a portion of which was captured on video and published by Univision in February — Mr. Miller often appears to be smirking.
“It’s a character?” Mr. Castillo said. “When you hear it more than once, when you hear it in private, when you hear it in public, that ‘character’ kind of fades away. That benefit of the doubt is gone.”
Mentors on the Right
Mr. Miller’s defenders have argued that Mr. Miller’s high school persona — more merry prankster than fearsome bomb thrower, in their view — should not diminish the seriousness of his beliefs. Mr. Miller has attributed his conservative awakening, in part, to encountering right-leaning writings on gun policy and other issues, including a 1994 book, “Guns, Crime and Freedom” by Wayne LaPierre, the National Rifle Association leader.
Mr. Miller has said he was also shaped by his school’s response to the attacks of Sept. 11, 2001, when he confronted what he believed to be excess political correctness and insufficient support for American military efforts. Among his causes: pressing administrators to require the daily recitation of the Pledge of Allegiance. (He prevailed.)
Mr. Miller found mentors in David Horowitz, the onetime “New Left” Marxist who evolved into a conservative author, and a radio host, Larry Elder, who booked Mr. Miller as a recurring guest. He courted local controversy by inviting both to campus for speeches.
“He was already reading Ayn Rand. He was already reading the Federalist Papers,” Mr. Elder said, describing Mr. Miller as effectively a fully formed ideologue by the time he contacted the radio host’s show. “It’s not an act. He believes what he believes.”
News articles have often described Mr. Miller as the product of liberals whose politics changed through sheer force of their son’s arguments. Public documents do support this timeline: Mr. Miller’s parents, Michael and Miriam, changed their registration to Republican from Democrat after Mr. Miller left for college, according to Los Angeles County records.
But some who knew the family at the time have challenged the suggestion that he was raised in a classically hard-left Southern California home.
Ms. Miller’s brother, David Glosser, said the elder Mr. Miller, a real estate investor, had longed skewed conservative on some issues, describing him as a “responsible, thoughtful sort of economic Republican” that Mr. Glosser contrasted with Mr. Trump.
Messages left for Mr. Miller’s parents were not returned.
At Santa Monica Synagogue, the Millers proved an awkward fit in the largely liberal Reform congregation, according to people who knew them then. The younger Mr. Miller — true to form — established himself as the perpetually debate-ready boy who most enjoyed taking on all comers in 10th-grade confirmation class. A group photo, with Mr. Miller grinning from the back row in a prayer shawl, still hangs in the hall.
“We did our best here,” said Mr. Miller’s rabbi, Jeff Marx, “to teach Jewish ethics and talk about our need to reach out to the strangers, to those less fortunate than we are.”
By then, the Miller family had suffered its own notable reversal of fortunes. Earthquake-related property damage had upended Michael Miller’s real estate business, forcing the family to eventually abandon its stately home in the city’s exclusive North of Montana neighborhood.
Some classmates have speculated that the move, which found the family in a new house a short distance from the grittier and far more ethnically diverse Pico neighborhood, helped shape Mr. Miller’s still-developing views of race and class as he wended through his teens.
But others have dismissed this theory, suggesting that the family’s plight should not be overstated. A visit on a recent weekday found a succession of Mercedes-Benzes and Lexuses gliding down the block, with a team of Latino workers tending to landscaping along the sidewalk.
“They still moved to a two-story house in Santa Monica,” said Taylor Brinckerhoff, a family friend of the Millers’ who often attended Passover dinners with them.
For fellow students, the most credible origin story for Mr. Miller remains the simplest.
Surely he believed what he was saying, or at least most of it. But he also seemed to grasp quickly that contrarianism could be its own reward in an ecosystem of the like-minded, a way to stand out among the egos and trust funds of a singular American school district.
“Confrontation was his sort of modus operandi,” said Mr. Rosmarin, the former Santa Monica high school newspaper editor, who now works for the American Civil Liberties Union. “I think it’s why he came to school in the morning.”
And there is little doubt that he subscribed early to a future tenet of Breitbart-era conservatism: If you are upsetting liberals, you are probably doing something right.
“That was you?” Andrew Breitbart, the founder of the far-right website that bears his name, asked Mr. Miller in 2011, according to three people present for the exchange, during a gathering at the Breitbart townhouse beside the Supreme Court.
When Mr. Miller’s history was mentioned, these people said, Mr. Breitbart instantly recalled the California teenager who had become something of a cult figure in right-wing news media for laying verbal waste to his high school.
Duke, and on to Washington
The megaphones only got louder, a function of timing and gumption.
As a student at Duke University, when the school became a national political minefield in 2006 after a black woman accused three white lacrosse players of rape, Mr. Miller sensed an opportunity.
Where most students and professors sided quickly with the alleged victim, Mr. Miller became the players’ most vocal defender on cable television, appearing on Fox News to accuse the prosecutor of a witch hunt long before the case collapsed.
“We are at a terrible dearth of intelligent, common-sense, courageous voices on campus,” Mr. Miller, then a senior, told Bill O’Reilly on his Fox show, taking something of a victory lap.
After graduating, Mr. Miller moved to Washington to work as press secretary for Representative Michele Bachmann of Minnesota. By 2009, he found his way to Senator Jeff Sessions of Alabama (Mr. Horowitz, the author, had introduced them), and he was eventually elevated to Mr. Sessions’s communications director.
In their years together, Mr. Miller positioned himself — and helped position Mr. Sessions, now the attorney general — inside the Republican Party’s burgeoning Breitbart wing, seizing on immigration as a central issue while bipartisan immigration legislation slithered through Congress in 2013.
Mr. Miller also found common cause with Mr. Bannon, who hoped to fashion the Breitbart News site into a battlefield for the so-called alt-right, a far-right fringe movement that often embraces an ideology of white nationalism. In 2014, the two helped propel a nearly anonymous House candidate in Virginia, Dave Brat, to a primary election victory over Eric Cantor, the majority leader at the time, in part by hammering Mr. Cantor as overly tolerant of illegal immigration. The race in many ways presaged the campaign of Mr. Trump, whose prospects Mr. Miller soon eyed with excitement.
“Trump gets it,” Mr. Miller wrote to friends weeks later, forwarding a Breitbart interview with Mr. Trump, who concluded that Mr. Cantor’s defeat owed to “his softness on immigration.”
“I wish he’d run for president,” Mr. Miller added of Mr. Trump.
When he did, Mr. Miller joined him early, before a vote had been cast in the primaries — and before Mr. Sessions became Mr. Trump’s most significant elected supporter. At rallies, Mr. Miller often warmed up crowds in his dark suits, his receding hairline slicked back. “We’re going to build that wall, and we’re going to build it out of love!” Mr. Miller promised.
Mr. Miller quickly grew comfortable with Mr. Trump’s impromptu style during the campaign, on more than one occasion ripping up a completed speech in the back of the candidate’s black S.U.V. because Mr. Trump had a change of heart on the way to an event.
And people close to both men say that more than anyone, Mr. Miller has grasped how to fuse the cadences of Mr. Trump’s own plain-spoken language with something loftier, at times scribbling notes on a piece of paper pressed to the side of a car window as he jotted down the president’s thoughts.
Occasionally, Mr. Miller has retained a public-facing role. In August, when the administration announced its support for a proposal to slash legal immigration, the White House briefing room belonged to him.
By the time the news conference was over, Mr. Miller had sparred with The New York Times, accused a CNN reporter of “cosmopolitan bias” and suggested that the poem associated with the Statue of Liberty (“Give me your tired, your poor, your huddled masses”) should not inform American immigration policy because it was not added to Liberty Island until 17 years after the statue’s unveiling.
As he spoke, Ms. Sanders, the press secretary, inched closer, sensing it was time to reclaim the microphone. But Mr. Miller seemed tickled by the combat.
“I think that went exactly as planned,” Mr. Miller said coyly, finally ceding the stage. “I think that was exactly what we were hoping to have happen.”