WASHINGTON — Shortly before midnight on Friday, and just hours after he had taken to Twitter to encourage Americans to “liberate” three Democratic-governed states from stay-at-home orders, President Trump reopened his Twitter app and went on another brief tear. He retweeted 11 posts by Charlie Kirk, a young right-wing provocateur with ties to the Trump family and a social media presence that attracts far more attention than some mainstream news organizations.

The tweets by Mr. Kirk, 26, who runs Turning Point USA, a conservative student group, hit just the right marks for the president. One tweet accused the World Health Organization of covering up the coronavirus outbreak, and upbraided Democrats for opposing the president’s decision to cut the group’s funding. Another claimed Democrats were appeasing Beijing and not doing enough to help Americans left jobless by the pandemic. A few covered some of the president’s longstanding grievances, such as the conviction of Roger Stone and claims of voter fraud. A well-worn conspiracy theory about Hunter Biden’s dealings with China even made an appearance.

Never mind that the W.H.O — which Mr. Kirk called “the Wuhan Health Organization,” after the city where the pandemic began — issued warnings about the virus early and often, and that a number of the other tweets similarly misconstrued facts. Mr. Kirk doesn’t always let facts get in the way of scoring points, and in recent months he has done as much as anyone to stoke conservative skepticism of the threat posed by Covid-19 and to use the pandemic as political cudgel.

In fact, Mr. Trump first introduced his more than 77 million Twitter followers to the phrase “China Virus” in a retweet of a post by Mr. Kirk on March 10 that linked two Trumpian obsessions: China and the border wall.

“Now more than ever, we need the wall. With China Virus spreading across the globe, the U.S. stands a chance if we can control our borders,” Mr. Kirk wrote.

Mixing, matching and twisting facts, Mr. Kirk has come to exemplify a new breed of political agitator that has flourished since the 2016 election by walking the line between mainstream conservative opinion and outright disinformation. It is a style that often seems modeled on that of Mr. Trump himself, and has propelled Mr. Kirk from student activist to leading voice on the right. His work is bankrolled by prominent Republican donors, and he has cultivated a powerful ally in the president’s eldest son, Donald Trump Jr.

The pandemic has showcased Mr. Kirk’s influence, providing him with ample fodder to stir up fellow conservatives against a full menu of enemies, real and perceived. In his zeal, Mr. Kirk even managed to get himself briefly banned from Twitter in late March, claiming that the drug hydroxychloroquine had proved “100% effective” in treating the virus (it has not), and that Michigan’s Democratic governor, Gretchen Whitmer, had threatened doctors who tried to use it (she had not). Rudolph W. Giuliani, the president’s lawyer, followed suit in his own tweet, directly quoting Mr. Kirk and getting his own account suspended.

Being banned from Twitter is a badge of honor among some conservatives, however, and it did little to stop Mr. Kirk, who declined an interview request for this article. Even as the president and his media allies have oscillated between dismissing the alarm over the virus as anti-Trump hysteria and acknowledging the gravity of the threat — with conspiracy theorists like Mike Cernovich calling for a “culture war cease-fire” — Mr. Kirk has not wavered.

Though he warned young people in March to take the virus seriously and not party on beaches, Mr. Kirk spent the days leading up to Easter arguing that social-distancing prohibitions against church services were part of a Democratic plot against Christianity. “This China Flu event has given state and local secularists in positions of authority the opportunity they have been waiting for,” he wrote in an essay for Newsweek, where he is a contributor.

China has remained a target for Mr. Kirk. He has echoed the Trump campaign’s attacks on former Vice President Joseph R. Biden Jr., the presumptive Democratic nominee, saying he is soft on China. Earlier this month, he repeated a baseless conspiracy theory that the authorities in Wuhan were burning patients.

“THIS is what the American media is defending,” he wrote on Twitter, exhorting his followers to repost his message and “expose the truth!”

A Useful Friendship

Mr. Kirk has not always been among the believers. As late as the 2016 Republican convention, he was quoted saying that he “was not the world’s biggest Donald Trump fan.”

But it was at the convention that Mr. Kirk, like much of the Republican Party, began falling in line. And it was there he first met Donald Trump Jr. Sensing an opportunity, Mr. Kirk offered to help bolster his standing with young conservatives. He then essentially trailed the younger Mr. Trump in the final months of the campaign, ingratiating himself with the family.

“I traveled the country for about 70 days straight carrying Donald Trump Jr.’s bags and getting his Diet Cokes,” Mr. Kirk told the conservative radio host Rush Limbaugh in February 2019. “Helping book flights and taking pictures and coordinating media, essentially being the youth director of the campaign and also being Don Jr.’s body man.”

The relationship has proved mutually beneficial as both men have constructed careers around the idea that left-wing culture has victimized and silenced conservatives. Mr. Kirk has used his Trump connections to raise Turning Point’s profile, and his own. Mr. Trump has used speaking engagements with Turning Point to burnish his own conservative bona fides.

The relationship had other benefits, too. Last fall, Turning Point purchased about 2,000 copies of Mr. Trump’s book, “Triggered: How the Left Thrives on Hate and Wants to Silence Us,” helping push it up best-seller lists.

The guests on Mr. Kirk’s podcast provide a useful measure of his influence: They have included Mark Meadows, the former congressman and now White House chief of staff, Senator Rick Scott of Florida, Senator Ted Cruz of Texas and other leading Republicans. His allies credit his ability to tap into anger and frustration felt by conservatives and turn that into messaging.

“Charlie has become such an influential figure in conservative politics because he has his finger on the pulse of the right,” said Andy Surabian, an adviser to Donald Trump Jr.

A Digital Native

Fox News stars like Sean Hannity and Tucker Carlson may attract more attention from the political and media establishments. But Mr. Kirk boasts an equally impressive reach, albeit among a far-younger audience — an important political quarry for the president.

Some of that reach has been built through Turning Point, which aims to bolster conservative politics on college campuses across the country. Mr. Kirk speaks often at college events; his group has secretly funneled money into student government elections and maintains what it calls a “Professor Watchlist” of teachers who, it alleges, discriminate against conservatives or advance left-wing propaganda.

But Mr. Kirk’s combative style truly thrives on social media. In the final two weeks of March, for instance, his Twitter posts about the coronavirus garnered far more “engagements” — a combination of likes, retweets, comments and other interactions — than those of mainstream news organizations like The New York Times and CNN. Conservative outlets like The Daily Caller have not even come close to matching Mr. Kirk’s level of engagement.

In that time, Mr. Kirk has argued that Democratic governors are using the coronavirus as an excuse to push for state funding of abortions, and claimed falsely that officials in Portland, Ore., where a handful of businesses were vandalized after the state issued a stay-at-home order, were releasing dangerous inmates from prisons and ordering the police to stop making arrests. “Democrat logic,” he said, was responsible for vandals “smashing windows & destroying businesses.”

And then, of course, there was his “China virus” tweet. The phrase had been growing in popularity among some on the right, and Mike Pompeo, the secretary of state, had been consistently referring to Covid-19 as the “Wuhan virus.” But the president had not used the phrase in public until he retweeted Mr. Kirk.

Mr. Trump quickly adopted the phrases “China virus” and “Chinese virus,” drawing the ire of critics who said the term promoted xenophobia. In late March, he went so far as to alter a set of prepared remarks, crossing out “coronavirus” and writing “China virus” in thick black Sharpie, though he has since backed off the term.

The White House, too, has appeared to join Mr. Trump in taking social media cues from Mr. Kirk. On March 16, Mr. Kirk tweeted a list of diseases named for geographic locations — including the West Nile virus, Ebola and Zika — and wrote, “It’s not xenophobic.”

Two days later, the White House came back with a remarkably similar tweet: “Spanish Flu. West Nile Virus. Zika. Ebola. All named for places.”

A Turning Point

Mr. Kirk grew up in Prospect Heights, Ill., a wealthy suburb of Chicago. His family was conservative but not particularly political, Mr. Kirk wrote in his 2016 book “Time for a Turning Point.”

His climb to prominence began in April 2012 when, as a high school senior, he wrote a story for Breitbart News arguing that teenagers were being indoctrinated by liberal textbooks. It was hardly a novel idea, but it earned Mr. Kirk an appearance on Fox Business Network and a speaking engagement at a nearby college. There, he was approached by Bill Montgomery, a retired entrepreneur who was impressed by his stage presence.

“You can’t go to college!” Mr. Montgomery later recalled telling Mr. Kirk. The pair founded Turning Point the following month.

Over the next few years, as Mr. Kirk began making regular appearances on Fox News, Turning Point’s profile grew, attracting tens of millions of dollars from the Republican establishment.

Though Turning Point is not required to disclose its financial backers, its roster of heavyweight conservative donors includes Foster Friess, an evangelical Christian businessman who provided the first big injection of cash; the foundation run by Bernard Marcus, co-founder of the Home Depot; and the foundation started by Richard and Helen DeVos, the in-laws of Betsy Devos, the education secretary. Its board members include Ginni Thomas, the wife of Supreme Court Justice Clarence Thomas.

Turning Point has also drawn controversy. A number of staff members have been fired for making racist and anti-Semitic comments, and the group has attracted support from white nationalists. Mr. Kirk has repeatedly insisted that Turning Point does not share their ideology or seek their backing.

What he mostly seems to enjoy is mixing it up in all comers, right or left. When white nationalists clashed with counterprotesters after he spoke at the University of Northern Colorado in 2018, Mr. Kirk tweeted, “Why free speech is awesome: these handful of radicals screamed at each other while hundreds of students filled our event!”

Some conservative groups have been sharply critical of Turning Point and Mr. Kirk. In March, the Charles Koch Foundation accused Turning Point of “inciting harassment against scholars” after Mr. Kirk tweeted a message encouraging students whose courses were moved online because of the coronavirus to record classes and expose left-wing professors.

Yet Mr. Kirk has only become more deeply embedded in the Republican establishment since Mr. Trump’s election. The president is fond of Mr. Kirk, according to current and former administration officials, and and one of his tweets on Friday praised Mr. Kirk’s new book, “The MAGA Doctrine.”

Last July, Mr. Kirk was invited to participate in a White House social media summit, ostensibly called to discuss the silencing of conservative voices. The guest list consisted mostly of Mr. Trump’s most ardent online supporters and included a number of fringe figures and conspiracy theorists.

“I think that’s a positive thing that the president is hearing new ideas and entertaining differences of opinion,” Mr. Kirk said in an interview at the time.