WASHINGTON (NYTIMES) - A loose network of conservative operatives allied with the White House is pursuing what they say will be an aggressive operation to discredit news organisations deemed hostile to United States President Donald Trump by publicising damaging information about journalists.

It is the latest step in a long-running effort by Mr 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 Mr Trump - in response to reporting or commentary that the White House's allies consider unfair to Mr Trump and his team or harmful to his re-election 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 Mr Arthur Schwartz, a combative 47-year-old conservative consultant who is a friend and informal adviser to Mr Donald Trump Jr, the president's eldest son. Mr 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," Mr Schwartz tweeted last 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 re-election 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 Mr Donald Trump Jr and, among others, Ms Katrina Pierson, a senior adviser to the Trump campaign, and quickly became the subject of a Breitbart interview with Ms 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 Mr Tim Murtaugh, the campaign's communications director.

The campaign is consistent with Mr 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 organisations 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 Mr Sam Nunberg, a former aide to Mr Trump who is a friend of Mr Schwartz.

Mr 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 Mr 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, he added. But an organised, 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."

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 Mr 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.

The operation's tactics were on display last week, seemingly in response to two pieces in the Times that angered Mr Trump's allies. The paper's editorial board published an editorial last Wednesday accusing Mr Trump of fomenting anti-Semitism, and the newsroom published a profile last Thursday morning of Ms 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 Ms 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 Mr 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".

Mr Schwartz tweeted a link to the Breitbart piece before 7am, which Mr 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 Senator Ted Cruz of Texas, joined in highlighting the report.

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

Mr 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," he said.

Like Mr 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.