It is the latest step in a long-running effort by Trump and his allies to undercut the influence of legitimate news reporting. Four people familiar with the operation described how it works, asserting that it has compiled dossiers of potentially embarrassing social media posts and other public statements by hundreds of people who work at some of the country’s most prominent news organisations.

The group has released information about journalists at CNN, The Washington Post and The New York Times — three outlets that have aggressively investigated Trump — in response to reporting or commentary that the White House’s allies consider unfair to Trump and his team or harmful to his reelection prospects.

Operatives have closely examined more than a decade’s worth of public posts and statements by journalists, the people familiar with the operation said. Only a fraction of what the network claims to have uncovered has been made public, the people said, with more to be disclosed as the 2020 election heats up. The research is said to extend to members of journalists’ families who are active in politics, as well as liberal activists and other political opponents of the president.

It is not possible to independently assess the claims about the quantity or potential significance of the material the pro-Trump network has assembled. Some involved in the operation have histories of bluster and exaggeration. And those willing to describe its techniques and goals may be trying to intimidate journalists or their employers.

But the material publicised so far, while in some cases stripped of context or presented in misleading ways, has proved authentic, and much of it has been professionally harmful to its targets.

It is clear from the cases to date that among the central players in the operation is Arthur Schwartz, a combative 47-year-old conservative consultant who is a friend and informal adviser to Donald Trump Jr, the president’s eldest son. Schwartz has worked with some of the right’s most aggressive operatives, including former Trump adviser Steve Bannon.

“If the @nytimes thinks this settles the matter we can expose a few of their other bigots,” Schwartz tweeted on Thursday in response to an apologetic tweet from a Times journalist whose anti-Semitic social media posts had just been revealed by the operation. “Lots more where this came from.”

The information unearthed by the operation has been commented on and spread by officials inside the Trump administration and reelection campaign, as well as conservative activists and right-wing news media such as Breitbart News. In the case of the Times editor, the news was first published by Breitbart, immediately amplified on Twitter by Donald Trump Jr and, among others, Katrina Pierson, a senior adviser to the Trump campaign, and quickly became the subject of a Breitbart interview with Stephanie Grisham, the White House press secretary and communications director.

The White House press office said that neither the president nor anyone in the White House was involved in or aware of the operation, and that neither the White House nor the Republican National Committee was involved in funding it.

The Trump campaign said it was unaware of, and not involved in, the effort, but suggested that it served a worthy purpose. “We know nothing about this, but it’s clear that the media has a lot of work to do to clean up its own house,” said Tim Murtaugh, the campaign’s communications director.

The campaign is consistent with Trump’s long-running effort to delegitimise critical reporting and brand the news media as an “enemy of the people.” The president has relentlessly sought to diminish the credibility of news organizations and cast them as politically motivated opponents.

Journalism, he said in a tweet last week, is “nothing more than an evil propaganda machine for the Democrat Party.”

The operation has compiled social media posts from Twitter, Facebook and Instagram, and stored images of the posts that can be publicised even if the user deletes them, said the people familiar with the effort. One said that the operation had unearthed potentially “fireable” information on “several hundred” people.

“I am sure there will be more scalps,” said Sam Nunberg, a former aide to Trump who is a friend of Schwartz.

Nunberg and others who are familiar with the campaign described it as meant to expose what they see as the hypocrisy of mainstream news outlets that have reported on the president’s inflammatory language regarding race.

“Two can play at this game,” he said. “The media has long targeted Republicans with deep dives into their social media, looking to caricature all conservatives and Trump voters as racists.”

But using journalistic techniques to target journalists and news organisations as retribution for — or as a warning not to pursue — coverage critical of the president is fundamentally different from the well-established role of the news media in scrutinising people in positions of power.

“If it’s clearly retaliatory, it’s clearly an attack, it’s clearly not journalism,” said Leonard Downie Jr, who was the executive editor of The Post from 1991 to 2008. Tension between a president and the news media that covers him is nothing new, Downie added. But an organized, wide-scale political effort to intentionally humiliate journalists and others who work for the news media is.

“It’s one thing for Spiro Agnew to call everyone in the press ‘nattering nabobs of negativism,’” he said, referring to the former vice president’s famous critique of how journalists covered President Richard Nixon. “And another thing to investigate individuals in order to embarrass them publicly and jeopardise their employment.”

AG Sulzberger, the publisher of the Times, said in a statement that such tactics were taking the president’s campaign against a free press to a new level.

“They are seeking to harass and embarrass anyone affiliated with the leading news organisations that are asking tough questions and bringing uncomfortable truths to light,” Sulzberger said. “The goal of this campaign is clearly to intimidate journalists from doing their job, which includes serving as a check on power and exposing wrongdoing when it occurs. The Times will not be intimidated or silenced.”

In a statement, a CNN spokesman said that when government officials, “and those working on their behalf, threaten and retaliate against reporters as a means of suppression, it’s a clear abandonment of democracy for something very dangerous.”

The operation is targeting the news media by using one of the most effective weapons of political combat — deep, laborious research into the public records of opponents to find contradictions, controversial opinions or toxic affiliations. The liberal group Media Matters for America helped pioneer close scrutiny of public statements by conservative media personalities.

Conservative operative James O’Keefe has twisted that concept in ways inconsistent with traditional journalistic ethics, using false identities, elaborate cover stories and undercover videos to entrap journalists and publicise embarrassing statements, often in misleading ways, to undercut the credibility of what he considers news media biased in favor of liberals.

In the case of the pro-Trump network, research into journalists is being deployed for the political benefit of the White House. It is targeting not only high-profile journalists who challenge the administration, but also anyone who works for any news organisation that members of the network see as hostile to Trump, no matter how tangential that job may be to the coverage of his presidency. And it is being used explicitly as retribution for coverage.

Some reporters have been warned that they or their news organisations could be targets, creating the impression that the campaign intended in part to deter them from aggressive coverage as well as to inflict punishment after an article has been published.

Trained as a lawyer, Schwartz has endeared himself to members of the president’s family by becoming one of their most aggressive defenders, known for badgering and threatening reporters and others he believes have wronged the Trumps.

He has publicly gone after Republicans he views as disloyal, including the former White House chief of staff Reince Priebus, about whom he admitted spreading an unsubstantiated rumor. He has called himself a “troll on Twitter,” which is where he has boasted of being aware of, or having access to, damaging information on dozens of journalists at CNN and the Times that could be deployed if those outlets ran afoul of Trump or his allies.

The operation’s tactics were on display last week, seemingly in response to two pieces in the Times that angered Trump’s allies. The paper’s editorial board published an editorial on Wednesday accusing Trump of fomenting anti-Semitism, and the newsroom published a profile on Thursday morning of Grisham, the new White House press secretary, which included unflattering details about her employment history.

One person involved in the effort said the pro-Trump forces, aware ahead of time about the coverage of Grisham, were prepared to respond. Early Thursday morning, soon after the profile appeared online, Breitbart News published an article that documented anti-Semitic and racist tweets written a decade ago by Tom Wright-Piersanti, who was in college at the time and has since become an editor on the Times’ politics desk. The Times said it was reviewing the matter and considered the posts “a clear violation of our standards.”

Schwartz tweeted a link to the Breitbart piece before 7 a.m., which Donald Trump Jr. retweeted to his 3.8 million followers — the first of about two dozen times that the president’s son shared the article or its contents. Other prominent Republicans, including Sen. Ted Cruz of Texas, joined in highlighting the report.

Breitbart’s article quoted several people or groups with close ties to Schwartz, including Richard Grenell, Trump’s ambassador to Germany, and the Zionist Organisation of America. It was written by the site’s Washington political editor, Matthew Boyle, whose relationship with Schwartz started when Bannon ran the website.

Boyle’s article included a reference to the Times profile of Grisham, which it characterized as “attacking White House Press Secretary Stephanie Grisham.” Wright-Piersanti was uninvolved in the editing of the article about Grisham.

The tweets revealed in the Breitbart article quickly spread to other conservative news media favoured by the president and his allies, including the radio shows of Rush Limbaugh and Mark Levin.

Wright-Piersanti apologised on Twitter on Thursday morning and deleted offensive tweets. Schwartz then issued his warning that he had further damaging information about Times employees.

Wright-Piersanti, 32, said the posts, posted when he was a college student with a Twitter following consisting mostly of personal acquaintances, were “my lame attempts at edgy humour to try to get a rise out of my friends.”

But he said “they’re not funny, they’re clearly offensive,” adding, “I feel deep shame for them, and I am truly, honestly sorry that I wrote these.”

He said he had forgotten about the tweets as he started a career in journalism.

“For my generation, the generation that came of age in the internet, all the youthful mistakes that you made get preserved in digital amber, and no matter how much you change and mature and grow up, it’s always out there, waiting to be discovered,” Wright-Piersanti said.

Like Wright-Piersanti, other targets of the pro-Trump network have been young people who grew up with social media and wrote the posts in question when they were in their teens or early 20s, in most cases before they became professional journalists.

A week after a White House reporter for CNN sparred with Trump during a news conference, Schwartz highlighted a tweet by the reporter from 2011, when the reporter was in college, that used an antigay slur. Other similar tweets quickly surfaced, and the reporter apologised, though Schwartz has continued to antagonise the reporter on Twitter.

In recent months, Schwartz highlighted a nearly decade-old tweet in which a reporter for the Post had repeated in an ambiguous manner a slur used by a politician.

In March, Schwartz tweeted a link to an article from Breitbart, written by Boyle, about a reporter from Business Insider whose Instagram account included anti-Trump references and a photograph of the reporter demonstrating against the president.

In July, around the time CNN published an article exposing old posts by a Trump appointee spreading suggestions that Barack Obama was a Muslim whose loyalty to the United States was in question, Schwartz resurfaced anti-Semitic tweets from 2011 by a CNN photo editor. Schwartz suggested that a CNN reporter who specializes in unearthing problematic archival content should “look into the social media activities of your employees.”

The tweets became the basis for several articles in conservative news outlets and hundreds of tweets from conservatives targeting the photo editor, Mohammed Elshamy, which did not stop even after he resigned under pressure from CNN and apologised.

“It felt like a coordinated attack,” said Elshamy, who said he had received death threats. “It was overwhelming.”

Elshamy, who is now 25, said he posted the tweets when he was 15 and 16 years old, growing up in Egypt, when he was still learning English and did not fully grasp the meaning of the words.

“I was repeating slogans heard on the streets during a highly emotional time in my nation’s history,” he said. “I believe that my subsequent work and views over the years redeems for the mistakes I made as a kid.”

While he said he understands “the severity and harm of my comments,” he questioned the motivation of the campaign that cost him his job. “It is a very dirty tactic that they are using to cause as much harm as they can to anyone who is affiliated with these media outlets,” he said. “It actually feels like a competition and every termination or vilification is a point for them.”

Bannon, at the time the head of Breitbart, oversaw the site’s efforts in 2015 to attack Megyn Kelly, then of Fox News, after she called out Trump for tweets disparaging women as “fat pigs,” “dogs” and “slobs.” In an interview, he said the work that Schwartz was undertaking should be seen as a sign that Trump’s supporters were committed to executing a frontal assault on news media they considered adversarial.

“A culture war is a war,” he said. “There are casualties in war. And that’s what you’re seeing.”