ON the day of President Donald Trump's inauguration, two poorly understood forces of the internet collided in a sort of bizarre death lock - a struggle that has manifested in the real world as Nazi-costumed dances in New York, a meticulously planned theft in rural Tennessee and last month, a raid on a British rooftop.

These forces are called 4chan and Shia LaBeouf.

LaBeouf is a Hollywood star who recently restyled himself as a highly meme-able performance artist - limiting his public utterances to a string of repeat tweets, for example, or showing up to a film festival with a paper bag on his head.

4chan is the magmatic underworld of the internet: an anonymous forum whose millions of users gave the world the delights of Rickrolling, the misogyny of Gamergate and the corruption of Pepe the Frog.

Lately, 4chan's vast energies have been spent disrupting a single webcam. LaBeouf's art group installed the camera outside a museum in New York on Jan. 20, inviting the public to join the star in chanting: "He will not divide us ... he will not divide us."

"He Will Not Divide Us" was supposed to last the duration of Trump's first term.

Almost instantly, 4chan users turned the live feed into hell's own reality show.

Dubbed "Season 1" on 4chan and associated forums, the New York live stream was forced to relocate after self-professed neo-Nazis and other disrupters kept making cameos - provoking LaBeouf until he was arrested and accused of assaulting a troll.

Since then, the struggle has shifted to Seasons 2 through 4 - in which trolls pursued the webcam across the United States, until the artists were forced to replace the public chanting with a live feed of a guarded flag, which forum users have twice found and tried to steal, most recently on a rooftop in Britain.

"We have been doing everything within our powers to maintain the work in the face of these efforts to silence it," the artist group, LaBeouf, Rönkkö & Turner, wrote to The Washington Post.

They called the disruptions "concerted efforts by far-right extremists, white supremacists and neo-Nazis to terrorize, deface, steal, and ultimately silence the work."

But like everything about art and 4chan, what's actually behind the trolling campaign is not so easy to define.

Not that there's anything ambiguous about a man shouting "Hitler did nothing wrong" into a camera outside the Museum of Moving Image. Or about dancing around LaBeouf in a Nazi officer's cap.

Many other disruptions, however, were more juvenile than offensive. Some were earnest speeches from Trump supporters or others who took offense to whatever LaBeouf and his partners were trying to say with the chants.

LaBeouf chased off disrupters repeatedly in January, before New York police arrested him on camera and charged him with misdemeanor assault. The charge was later dropped for lack of evidence, but the museum evicted the project due to safety concerns.

The webcam relocated to a square in Albuquerque in February, and lasted about a week before similar incidents caused the artists to pack up.

Every disruption to the "He Will Not Divide Us" project has been archived by people on the anonymous forums, and organized on a swastika-themed website that reimagines the art project as a TV show.

Seasons are named "Escape from Jew York" and "HWNDU Albuquerque," for example, and anyone who has interrupted a chant is written up as a minor celebrity.

The most famous of these is likely a 23-year-old software engineer named Eugene Li - known on the forums as "Uncle Chang" for a speech he made in front of the New York webcam one night.

"I used to just be an American, now I'm a person of color, perpetually oppressed by the evil white men," said Li, his Asian features obvious in the streetlight. "Because I disagreed with you, I'm an Uncle Tom, an Uncle Chang."

A small crowd of friends cheered him on in the cold.

"If I'm a Nazi, then sieg heil, motherf---ers," Li said.

Nearly 20 million people on Facebook watched Li's second speech following riots at the University of California at Berkeley, when he condemned liberals for "normalizing violence."

Li has been browsing 4chan since he was a child, he told The Post.

"Every board's culture is a mix of irony and genuine whatever," he said. On the political boards driving the anti-LaBeouf campaigns, that confounding mix often takes the form of racial slurs.

Li hoped his own "sieg heil" was obviously ironic, he said - a protest against "how much the left had started policing language."

Since then, he has become personally acquainted with about 20 anti-LaBeouf trolls, including the author of the swastika Wiki.

"None of them were genuine white supremacists or Nazis," he insisted.

These are not convincing defenses to Whitney Phillips, a researcher who has spent a decade studying 4chan.

"A lot of them see themselves as pushing back against the man; the parallel falls apart as soon as you pay attention to what they're saying," said Phillips, a professor of literary studies at Mercer University and the co-author of a forthcoming book on Internet antagonists.

"Some of it is absurdist on its face, but it gets so ugly so fast."

In the campaign against LaBeouf, Phillips saw many of the same elements that drove the Gamergate attacks on women a couple of years ago, or "swatting," a potentially lethal prank in which police are tricked into raiding an innocent target's house.

"These things have been around for ages," she said. "They've been brought together in this new sort of way, this new sort of Trump-infused era."

How LaBeouf ended up a target is a story almost as mysterious as the motivations of a 4chan board.

A Disney child star who gained celebrity for the "Transformers" series and similar blockbusters, the performer was disgraced in 2012, when he wrote and directed a short film revealed to contain plagiarized material.

From there, The Post once wrote, "LaBeouf's life seemed to become an endless spectacle of artistic statements that left many frustrated."

In collaboration with the same artists involved in the current project - Nastja Sade Ronkko and Luke Turner - LaBeouf wore a bag on his head to the Berlin Film Festival in 2014.

He repeatedly tweeted the bag's message, "I Am Not Famous Anymore," and in a later project filmed himself watching every one of his movies for hours.

Most of this work was not obviously political.

And - somewhat confusingly - LaBeouf's group insists "He Will Not Divide Us" is not either, despite timing it to Trump's presidency.

In any event, 4chan had all the material it needed by the time the project launched.

After the webcam was shut down in New York and New Mexico, in early March, the artists replaced the chanting with a flag bearing the same message.

The webcam, once open to all, would be trained on the flag against an empty sky in an undisclosed location.

This, of course, was immediately taken as a challenge on 4chan.

The forum pages turned into a detective game as users studied every scant clue in the footage - cross referencing passing airplanes with known flight paths, and studying constellations after dark to triangulate the flag's location.

They got an assist when LaBeouf was photographed at a diner in Greeneville, Tennessee, and ended up in the local newspaper.

"Continued exchanges on 4chan.org and Twitter indicate at least one user traveled to the general area identified as the flag's likely placement," the Greenville Sun reported. "The person honked their vehicle's horn while driving around until the sound was picked up by the live-stream camera."

The flag's undisclosed location was in fact the backyard of a woman who knew the artists and had agreed to host it.

"It was just a little performance art piece," she told the Sun, after reporting to police two vehicles trespassing on her property and a small fire in her field, started "after fireworks were shot into her yard."

The morning after the fire, the artists' live stream showed the flag being lowered and a Trump hat run up the flagpole.

So much for Season 3.

"It's not even political anymore," said Li, who now writes about 4chan exploits on his website. "It's the world's largest capture the flag game. ... It's really funny how a bunch of nobodies on the internet can mess with a multimillionaire."

But Li said he hadn't heard about the fire, which disturbed him. "There's so many involved," he said. "There will be one or two people that take things that far."

Claiming that the United States was no longer safe for an art project tied to an American president, the collective relocated the flag to the top of an arts center in Liverpool late last month.

Within hours, schematics purporting to show the center's floor plans were uploaded to 4chan and 8chan, along with instructions on how to break into the building, get to the roof and steal the flag.

Before a single day had passed, some did just that, and police told the center to remove the flag.

So the live stream ended, again, and 4chan celebrated, again.

The artists did not answer questions about their next plans for the project, or how they intended to stop the trolling.

On 4chan, the forums are already bubbling with rumors of Season 5.