Ruth Fremson/The New York Times

Linda Sarsour awoke on Jan. 23, 2017, logged onto the internet, and felt sick.

The weekend before, she had stood in Washington at the head of the Women’s March, a mobilization against President Donald J. Trump that surpassed all expectations. Crowds had begun forming before dawn, and by the time she climbed up onto the stage, they extended farther than the eye could see.

More than four million people around the United States had taken part, experts later estimated, placing it among the largest single-day protests in the nation’s history.

But then something shifted, seemingly overnight. What she saw on Twitter that Monday was a torrent of focused grievance that targeted her. In 15 years as an activist, largely advocating for the rights of Muslims, she had faced pushback, but this was of a different magnitude. A question began to form in her mind: Do they really hate me that much?

That morning, there were things going on that Ms. Sarsour could not imagine.

More than 4,000 miles away, organizations linked to the Russian government had assigned teams to the Women’s March. At desks in bland offices in St. Petersburg, using models derived from advertising and public relations, copywriters were testing out social media messages critical of the Women’s March movement, adopting the personas of fictional Americans.

They posted as Black women critical of white feminism, conservative women who felt excluded, and men who mocked participants as hairy-legged whiners. But one message performed better with audiences than any other.

It singled out an element of the Women’s March that might, at first, have seemed like a detail: Among its four co-chairs was Ms. Sarsour, a Palestinian American activist whose hijab marked her as an observant Muslim.

Credit…Theo Wargo/Getty Images

Over the 18 months that followed, Russia’s troll factories and its military intelligence service put a sustained effort into discrediting the movement by circulating damning, often fabricated narratives around Ms. Sarsour, whose activism made her a lightning rod for Mr. Trump’s base and also for some of his most ardent opposition.

One hundred and fifty-two different Russian accounts produced material about her. Public archives of Twitter accounts known to be Russian contain 2,642 tweets about Ms. Sarsour, many of which found large audiences, according to an analysis by Advance Democracy Inc., a nonprofit, nonpartisan organization that conducts public-interest research and investigations.

Many people know the story about how the Women’s March movement fractured, leaving lasting scars on the American left.

fragile coalition to begin with, it headed into crisis over its co-chairs’ association with Louis Farrakhan, the Nation of Islam leader, who is widely condemned for his antisemitic statements. When this surfaced, progressive groups distanced themselves from Ms. Sarsour and her fellow march co-chairs, Carmen Perez, Tamika Mallory and Bob Bland, and some called for them to step down.

But there is also a story that has not been told, one that only emerged years later in academic research, of how Russia inserted itself into this moment.

For more than a century, Russia and the Soviet Union sought to weaken their adversaries in the West by inflaming racial and ethnic tensions. In the 1960s, K.G.B. officers based in the United States paid agents to paint swastikas on synagogues and desecrate Jewish cemeteries. They forged racist letters, supposedly from white supremacists, to African diplomats.

They did not invent these social divisions; America already had them. Ladislav Bittman, who worked for the secret police in Czechoslovakia before defecting to the United States, compared Soviet disinformation programs to an evil doctor who expertly diagnoses the patient’s vulnerabilities and exploits them, “prolongs his illness and speeds him to an early grave instead of curing him.”

A decade ago, Russia’s president, Vladimir V. Putin, oversaw a revival of these tactics, seeking to undermine democracies around the world from the shadows.

Social media now provided an easy way to feed ideas into American discourse, something that, for half a century, the K.G.B. had struggled to do. And the Russian government secretly funneled more than $300 million to political parties in more than two dozen countries in an effort to sway their policies in Moscow’s favor since 2014, according to a U.S. intelligence review made public last week.

What effect these intrusions had on American democracy is a question that will be with us for years. It may be unanswerable. Already, social media was amplifying Americans’ political impulses, leaving behind a trail of damaged communities. Already, trust in institutions was declining, and rage was flaring up in public life. These things would have been true without Russian interference.

But to trace the Russian intrusions over the months that followed that first Women’s March is to witness a persistent effort to make all of them worse.

Credit…James Hill for The New York Times

In early 2017, the trolling operation was in its imperial phase, swelling with confidence.

Accounts at the Internet Research Agency, an organization based in St. Petersburg and controlled by a Putin ally, had boasted of propelling Mr. Trump to victory. That year, the group’s budget nearly doubled, according to internal communications made public by U.S. prosecutors. More than a year would pass before social media platforms executed sweeping purges of Russian-backed sock-puppet accounts.

For the trolls, it was a golden hour.

Under these auspicious conditions, their goals shifted from electoral politics to something more general — the goal of deepening rifts in American society, said Alex Iftimie, a former federal prosecutor who worked on a 2018 case against an administrator at Project Lakhta, which oversaw the Internet Research Agency and other Russian trolling operations.

“It wasn’t exclusively about Trump and Clinton anymore,” said Mr. Iftimie, now a partner at Morrison Foerster. “It was deeper and more sinister and more diffuse in its focus on exploiting divisions within society on any number of different levels.”

There was a routine: Arriving for a shift, workers would scan news outlets on the ideological fringes, far left and far right, mining for extreme content that they could publish and amplify on the platforms, feeding extreme views into mainstream conversations.

Artyom Baranov, who worked at one of Project Lakhta’s affiliates from 2018 to 2020, concluded that his co-workers were, for the most part, people who needed the money, indifferent to the themes they were asked to write on.

“If they were assigned to write text about refrigerators, they would write about refrigerators, or, say, nails, they would write about nails,” said Mr. Baranov, one of a handful of former trolls who have spoken on the record about their activities. But instead of refrigerators and nails, it was “Putin, Putin, then Putin, and then about Navalny,” referring to Aleksei Navalny, the jailed opposition leader.

The job was not to put forward arguments, but to prompt a visceral, emotional reaction, ideally one of “indignation,” said Mr. Baranov, a psychoanalyst by training, who was assigned to write posts on Russian politics. “The task is to make a kind of explosion, to cause controversy,” he said.

When a post succeeded at enraging a reader, he said, a co-worker would sometimes remark, with satisfaction, Liberala razorvala. A liberal was torn apart. “It wasn’t on the level of discussing facts or giving new arguments,” he said. “It’s always a way of digging into dirty laundry.”

Feminism was an obvious target, because it was viewed as a “Western agenda,” and hostile to the traditional values that Russia represented, said Mr. Baranov, who spoke about his work in hopes of warning the public to be more skeptical of material online. Already, for months, Russian accounts purporting to belong to Black women had been drilling down on racial rifts within American feminism:

“White feminism seems to be the most stupid 2k16 trend”

“Watch Muhammad Ali shut down a white feminist criticizing his arrogance”

“Aint got time for your white feminist bullshit”

“Why black feminists don’t owe Hillary Clinton their support”

“A LIL LOUDER FOR THE WHITE FEMINISTS IN THE BACK”

In January 2017, as the Women’s March drew nearer, they tested different approaches on different audiences, as they had during the run-up to the 2016 presidential election. They posed as resentful trans women, poor women and anti-abortion women. They dismissed the marchers as pawns of the Jewish billionaire George Soros.

And they derided the women who planned to participate, often in crudely sexual terms. In coordination, beginning on Jan. 19, 46 Russian accounts pumped out 459 original suggestions for #RenameMillionWomenMarch, a hashtag created by a right-wing podcaster from Indiana:

The Why Doesn’t Anybody Love Me March

The Strong Women Constantly Playing the Victim March

The Lonely Cat Lady March

The Cramp Camp

The Bearded Women Convention

Broken Broads Bloviating

The Liberal Trail of Tears

Coyote Ugly Bitchfest

In the meantime, another, far more effective line of messaging was developing.

As one of the four co-chairs of the Women’s March, Ms. Sarsour came with a track record — and with baggage.

The daughter of a Palestinian American shopkeeper in Crown Heights, she had risen to prominence as a voice for the rights of Muslims after 9/11. In 2015, when she was 35, a New York Times profile anointed her — a “Brooklyn Homegirl in a Hijab” — as something rare, a potential Arab American candidate for elected office.

In 2016, Senator Bernie Sanders featured her at a campaign event, a stamp of approval from one of the country’s most influential progressives. That troubled pro-Israel politicians in New York, who pointed to her support for the Boycott, Divestment and Sanctions movement, which seeks to secure Palestinian rights by isolating Israel. Critics of the movement contend that it threatens Israel’s existence.

Rory Lancman, then a city councilman from Queens, recalls his growing alarm as she began to appear regularly at events for left-wing causes unrelated to Israel, like fair wages, where, he felt, “her real agenda was trying to marry an anti-Israel agenda with different progressive causes.”

The news that Ms. Sarsour was among the leaders of the Women’s March, said Mr. Lancman, a Democrat, struck him as “heartbreaking — that’s the word — that antisemitism is tolerated and rationalized in progressive spaces.”

That was politics as usual, and Ms. Sarsour was accustomed to it: the long-running feud among Democrats over the implications of criticizing Israel.

But 48 hours after the march, a shift of tone occurred online, with a surge of posts describing Ms. Sarsour as a radical jihadi who had infiltrated American feminism. Ms. Sarsour recalls this vividly, because she woke to a worried text message from a friend and glanced at Twitter to find that she was trending.

Not all of this backlash was organic. That week, Russian amplifier accounts began circulating posts that focused on Ms. Sarsour, many of them inflammatory and based on falsehoods, claiming she was a radical Islamist, “a pro-ISIS Anti USA Jew Hating Muslim” who “was seen flashing the ISIS sign.”

Some of these posts found a large audience. At 7 p.m. on Jan. 21, an Internet Research Agency account posing as @TEN_GOP, a fictional right-wing American from the South, tweeted that Ms. Sarsour favored imposing Shariah law in the United States, playing into a popular anti-Muslim conspiracy theory that Mr. Trump had helped to popularize on the campaign trail.

This message took hold, racking up 1,686 replies, 8,046 retweets and 6,256 likes. An hour later, @PrisonPlanet, an influential right-wing account, posted a tweet on the same theme. The following day, nearly simultaneously, a small army of 1,157 right-wing accounts picked up the narrative, publishing 1,659 posts on the subject, according to an analysis conducted by the online analytics firm Graphika on behalf of The Times.

Vladimir Barash, Graphika’s chief scientist, said the pattern of interference was “strategically similar” to troll activity targeting the vast anti-Putin protests of 2011 and 2012, with sock-puppet accounts “similarly trying to hijack the conversation, sometimes succeeding.”

“There is some circumstantial evidence that they learned in a domestic context and then tried to replicate their success in a foreign context,” Dr. Barash said.

Things were changing on the ground in New York. At the Arab American Association of New York, the nonprofit immigrant advocacy organization Ms. Sarsour ran in Bay Ridge, hate mail began to pour in — postcards, handwritten screeds on notebook paper, her photo printed out and defaced with red X’s.

“This was an entirely new level, and it felt weird, because it was coming from all over the country,” said Kayla Santosuosso, then the nonprofit’s deputy director, who remembers bringing the mail to Ms. Sarsour in shoe boxes. Ms. Sarsour, worried that she had become “a liability,” stepped down from her position there that February.

By the spring, the backlash against Ms. Sarsour had developed into a divisive political sideshow, one that easily drowned out the ideas behind the Women’s March. “It was like an avalanche,” she said. “Like I was swimming in it every day. It was like I never got out of it.”

When she was invited to appear as a graduation speaker at the City University of New York’s graduate school of public health, the furor began weeks in advance. It caught the attention of the far-right polemicist Milo Yiannopoulos, who traveled to New York for a protest that attracted, as a Times reporter wrote, “a strange mix, including right-leaning Jews and Zionists, commentators like Pamela Geller, and some members of the alt-right.”

“Linda Sarsour is a Shariah-loving, terrorist-embracing, Jew-hating, ticking time bomb of progressive horror,” Mr. Yiannopoulos told the crowd.

Ms. Sarsour recalls the period leading up to the graduation speech as particularly stressful. As it approached, she had visions of a figure coming out of the shadows to kill her, “some poor, like, deranged person who was consumed by the dark corners of the internet, who would be fueled by hate.”

Russian troll accounts were part of that clamor; beginning more than a month before her speech, a handful of amplifier accounts managed by Russia’s largest military intelligence agency, the G.R.U., circulated expressions of outrage at her being selected, often hashtagged #CancelSarsour.

When Mr. Yiannopoulos spoke, @TEN_GOP tweeted the juiciest phrases — the “ticking time bomb of progressive horror” line — and racked up 3,954 retweets and 5,967 likes.

Her graduation speech passed without incident. Then the trolls waited, it seems, for her to say or do something divisive. And that happened in early July, when, emboldened after her C.U.N.Y. appearance, she urged a Muslim audience outside Chicago to push back against unjust government policies, calling it “the best form of jihad.”

In Islam, the word “jihad” can denote any virtuous struggle, but in the American political context it is inextricable from the concept of holy war. A more pragmatic politician might have avoided using it, but Ms. Sarsour was feeling like her old self. “That’s who I am in real life,” she said. “I’m from Brooklyn, and I’m Palestinian. It’s my personality.”

To the Russian trolls, it was an opportunity.

The following week, Russian accounts dramatically increased their volume of messaging about Ms. Sarsour, producing 184 posts on a single day, according to Advance Democracy Inc.

Once again, the audience responded: When @TEN_GOP tweeted, “linda sarsour openly calls for muslims to wage jihad against trump, please look into this matter,” it received 6,222 retweets and 6,549 likes. The accounts sustained an intense focus on her through July, producing 894 posts over the next month and continuing into the autumn, the group found.

And once again, the backlash spilled out from social media. Protesters camped outside the kosher barbecue restaurant where her brother, Mohammed, worked as a manager, demanding that he be fired. He left the job, and, eventually, New York.

Her mother opened a package that arrived in the mail and screamed: It was a bizarre self-published book, titled “A Jihad Grows in Brooklyn,” that purported to be Ms. Sarsour’s autobiography and was illustrated with family photographs.

“I mean, just imagine,” Ms. Sarsour said, “every day that you woke up, you were a monster.”

Credit…Erin Scott/Reuters

It is maddeningly difficult to say with any certainty what effect Russian influence operations have had on the United States, because when they took hold they piggybacked on real social divisions. Once pumped into American discourse, the Russian trace vanishes, like water that has been added to a swimming pool.

This creates a conundrum for disinformation specialists, many of whom say the impact of Russian interventions has been overblown. After the 2016 presidential election, blaming unwelcome outcomes on Russia became “the emotional way out,” said Thomas Rid, author of “Active Measures: The Secret History of Disinformation and Political Warfare.”

“It’s playing a trick on you,” said Dr. Rid, a professor at Johns Hopkins University School of Advanced International Studies. “You become a useful idiot if you ignore effective info ops. But also if you talk it up by telling a story, if you make it more powerful than it is. It’s a trick.”

The divisions within the Women’s March existed already.

Internal disputes about identity and antisemitism had strained the group from its early days, when one of its organizers, Vanessa Wruble, who is Jewish, was pushed out after what she described as tense conversations with Ms. Perez and Ms. Mallory about the role of Jews in structural racism. Ms. Perez and Ms. Mallory have disputed that account.

And discomfort with Ms. Sarsour had dampened enthusiasm among some Jewish progressives, said Rachel Timoner, the senior rabbi of Congregation Beth Elohim in Park Slope, Brooklyn.

She recalled stepping up to defend Ms. Sarsour against “racist and Islamophobic” attacks, only to find, each time, that a new firestorm would arise, often resulting from something inflammatory and “ultimately indefensible” Ms. Sarsour had said.

As the months wore on, Rabbi Timoner said, Jews began asking themselves whether they were being excluded from progressive movements.

In 2018, a new internal crisis was triggered by Ms. Mallory’s attendance at Saviours’ Day, an annual gathering of the Nation of Islam led by Mr. Farrakhan.

Ms. Mallory grew up in Harlem, where many viewed the Nation of Islam and its founder positively, as crusaders against urban violence. Pressured to disavow Mr. Farrakhan, she refused, though she said she did not share his antisemitic views. After her son’s father was murdered, she explained, “it was the women of the Nation of Islam who supported me.”

“I have always held them close to my heart for that reason,” she said.

After that, the fabric of the coalition tore, slowly and painfully. Ms. Sarsour and Ms. Perez stuck by Ms. Mallory, and before long, progressive groups began distancing themselves from all three. Under intense pressure to step down as the leaders, Ms. Sarsour, Ms. Perez, and a third co-chair, Bob Bland, did so in 2019, a move they say was long planned.

Russian accounts boosted their output around Mr. Farrakhan and the Women’s March leaders that spring, posting 10 or 20 times a day, but there is no evidence that they were a primary driver of the conversation.

Around this time, we largely lose our view into Russian messaging. In the summer of 2018, Twitter suspended 3,841 accounts traced to the Internet Research Agency, preserving 10 million of their tweets so they could be studied by researchers. A few months later, the platform suspended and preserved the work of 414 accounts produced by the G.R.U., the military intelligence agency.

With that, a chorus of voices went silent — accounts that, for years, had helped shape American conversations about Black Lives Matter, the Mueller investigation and NFL players kneeling during the national anthem. The record of the messaging around the Women’s March breaks off there, too, frozen in time.

Russia’s exploitation of Ms. Sarsour as a wedge figure should be understood as part of the history of the Women’s March, said Shireen Mitchell, a technology analyst who has studied Russian interference in Black online discourse.

Russian campaigns, she said, were adept at seeding ideas that flowed into mainstream discourse, after which, as she put it, they could “just sit and wait.”

“It’s the priming of all that, starting from the beginning,” said Ms. Mitchell, the founder of Stop Online Violence Against Women. “If those thousand tweets hit a division between the groups that matter, if they open and allow that division, it’s no longer a crack. It becomes a valley.”

Others saw Russia’s role as marginal, tinkering around the edges of a necessary American discussion.

“It’s a shame that Linda Sarsour damaged that movement by trying to inject into it noxious ideas that had no reason to be part of the Women’s March,” said Mr. Lancman, the former city councilman. “Unfortunately,” he added, Russians “seem very adept at exploiting these fissures.”

Rabbi Timoner sounded sad, recalling all that had happened. The wounds that opened up between progressives that year have never quite healed, she said.

“There is so much Jewish pain here,” she said. “Those Russian bots were poking at that pain.”

The Women’s March continued under new leadership, but during the months of controversy, many women who had been galvanized by the first march drifted away.

“I can’t remember all the negative stories, I just remember that there were so many of them,” said Jennifer Taylor-Skinner, a Seattle woman who, after the 2017 march, quit her job at Microsoft and founded “The Electorette,” a podcast geared toward progressive women. She hasn’t ever recaptured that feeling of unity.

“Just thinking about it, I still feel a bit unmoored from any central movement,” she said. “There was a coalition possibly forming here that has been broken up.”

Ms. Sarsour, 42, was back in her old office in Bay Ridge this past spring, five years after the first Women’s March, when she learned, from a reporter, that the Russian government had targeted her.

She is seldom invited to national platforms these days, and when she is, protests often follow. Whatever buzz there was around her as a future political candidate has quieted. She knows how she is seen, as a polarizing figure. She has adjusted to this reality, and sees herself more as an activist, in the mold of Angela Davis.

“I’m never going to get a real job,” at a major nonprofit or a corporation, she said. “That’s the kind of impact that these things have on our lives.”

Data on Russian messaging around the Women’s March first appeared late last year in an academic journal, where Samantha R. Bradshaw, a disinformation expert at American University, reviewed state interference in feminist movements.

She and her co-author, Amélie Henle, found a pattern of messaging by influential amplifier accounts that sought to demobilize civil society activism, by pumping up intersectional critiques of feminism and attacking organizers.

Movements, Dr. Bradshaw argues, are fragile structures, often unprepared to weather well-resourced state-backed sabotage campaigns, especially when combined with algorithms that promote negative content. But healthy social movements are essential to democracies, she said.

“We’re not going to have a robust public sphere if nobody wants to organize protests,” she said.

Ms. Sarsour isn’t an academic, but she understood it well enough.

“Lord have mercy,” she said, glancing over Dr. Bradshaw’s findings.

Ms. Sarsour tried to get her head around it: All that time, the Russian government had been thinking about her. She had long had a sense of where her critics came from: the American right wing, and supporters of Israel. A foreign government — that was something that had never occurred to her.

“To think that Russia is going to use me, it’s much more dangerous and sinister,” she said. “What does Russia get out of leveraging my identity, you know, to undermine movements that were anti-Trump in America — I guess —” she paused. “It’s just, wow.”

Understanding what Russian trolls did would not change her position.

Still, it helped her understand that time in her life, when she had been at the center of a storm. It wasn’t just her fellow countrymen hating her. It wasn’t just her allies disavowing her. That had happened. But it wasn’t the whole story.

She placed a call to Ms. Mallory.

“We weren’t crazy,” she said.