The images the Anti-Defamation League considers symbols of hate are often historically fraught: the swastika, the Confederate flag, the Ku Klux Klan's burning cross. Now they have company from a green cartoon frog.

The ADL, a Jewish group that fights anti-Semitism and other forms of hate, just added Pepe the Frog to its database of hate symbols.

Pepe the Frog has been around the internet for years. Just a year ago he was so innocuous that celebrities like Katy Perry could tweet him without fear of backlash. But more recently, Pepe has morphed into something more insidious — a symbol embraced by the white nationalist alt-right, many of whom hang out on the forums where Pepe first originated years ago.

Pepe made the news recently when Donald J. Trump Jr. posted a photoshopped image of "The Deplorables" — featuring his father, Donald Trump, and his surrogates — he meant to mock Hillary Clinton’s comments calling Trump’s supporters "racist, sexist, homophobic, xenophobic, Islamophobic, you name it."

But the inclusion of Pepe the Frog suggested to many people that Trump was throwing his lot in with exactly the supporters Clinton was criticizing, the online trolls who, among other things, bombard journalists critical of Trump with anti-Semitic frog memes.

"That cartoon frog is more sinister than you might realize," Clinton’s campaign wrote, calling him a "symbol associated with white supremacy."

Pepe the Frog, in other words, is a dog whistle for the internet age, when the memes candidates post circulate far more broadly than any speech they ever make. Donald Trump Jr. says he didn’t have any idea what the frog meant. But his father, more than any other presidential candidate, has embraced the ethos of the rumor swamps of the internet. The trolls who love him back, in turn, have turned Pepe the Frog into his mascot.

How Pepe the Frog became a symbol of white nationalism

Like so many stories on the internet, this tale begins with 4chan, the vast, anonymous forum that first popularized Pepe and, eight years later, tied him to white nationalism.

The forum — which Vox’s Timothy Lee once described as the "Mos Eisley cantina of the internet" — spawned the hacker collective Anonymous and hosted leaked celebrity nude photos. It was one place where Gamergate activists organized. But because 4chan was a message board based around images long before communicating with images on social media was common, it’s also been the birthplace for many memes, including LOLCats, Rickrolling, and, yes, Pepe the frog.

Pepe began as a character in Boy’s Club, a comic that started on MySpace in 2005 by cartoonist Matt Furie. Boy’s Club was filled with stoner humor — Pepe and his three friends, a dog, a bear, and a wolf, are roommates who spend most of their time high — and the panels eventually began to stand on their own as memes. One in particular, a comic from 2008 about Pepe dropping his pants to pee and explaining it by saying, "Feels good man," became ubiquitous on 4chan.

Originally in black and white, Pepe was colored green. Users created smug frogs and sad frogs and angry frogs.

"Pepe, with his face, he’s got these large, expressive eyes with puffy eyelids and big rounded lips, I just think that people reinvent him in all these different ways," Furie told the Atlantic’s Adam Serwer. "It’s kind of a blank slate. It’s just out of my control, what people are doing with it."

Eventually, like many endlessly remixable memes, Pepe crossed over to more mainstream corners of the internet. Katy Perry tweeted a Pepe meme to complain about jet lag:

Australian jet lag got me like pic.twitter.com/kriAAd6mZe — KATY PERRY (@katyperry) November 8, 2014

By 2015, Pepe was the most reblogged meme on Tumblr, recognizable in all kinds of lowest-common-denominator jokes:

Me Rn. (@im6foot5if_you_were_wondering) A photo posted by Elliot Tebele (@fuckjerry) on Mar 6, 2016 at 6:43pm PST

And even prom invitations:

this is GREAT !!!!!! pic.twitter.com/kSLuoVezom — pepe the frog meme (@thefrogmeme) April 25, 2015

Then the Pepe trend got weirder with the phenomenon of "rare Pepes" — images of Pepe that were newer, weirder, and sometimes offensive. The basic idea was that images of Pepe the Frog had become too common. It was a way for the forums where the joke originated to begin to reclaim it:

The "rare Pepes" craze is layered in irony and in-jokes and is basically impenetrable, so we’re not going to get into it very deeply here. The main effect was that it revived Pepe on 4chan — and, at times, as part of offensive images — at a time when the site was becoming a hub for Trump support and members of the alt-right.

4chan loves Pepe the frog, Donald Trump, and the "alt-right"

The alt-right movement — a coalition of white supremacists and reactionaries who believe in rejecting democracy — has provided such visible support for Trump that Hillary Clinton devoted an entire speech to it.

The alt-right is a broad movement. It includes paleoconservatives, isolationists who were frequently anti-Semitic and were generally forced out of the conservative movement in the 1990s. Its intellectual underpinnings are from "reactionaries" who argue that democracy is flawed, that black people may well be genetically inferior to whites, and that the present is worse than the past. Those parts of the movement tend to communicate with lengthy essays, not with memes, and they’re not necessarily Trump supporters, as Vox’s Dylan Matthews reported.

But the alt-right also includes what BuzzFeed’s Joseph Bernstein dubbed the "chanterculture," which, he wrote, "combines age-old racist and sexist rhetoric with bleeding-edge meme culture and technology," mixing opposition to growing racial and gender equality with irony so heavy that it can be hard to tell if they’re really serious. Milo Yiannopoulos, the right-wing provocateur and Gamergate supporter, is the most prominent member of this branch of the alt-right.

The politics forum on 4chan, /Pol/, is ground zero for this rhetoric. Perhaps unsurprisingly, /pol/ is also aflame with support for Donald Trump. "It was how much asshurt he causes to others," one 4chan poster wrote in a post preserved on Reddit:

The schadenfreude is so funny that it digs a hole in you, and soon you can’t stop laughing — and then, because you’ve been laughing with him for a while, he begins to grow on you, and you hear what he actually says, and suddenly, because you are predisposed to like him because you’re both laughing at Jeb Bush, you find yourself supporting him, even if technically your political ideas don’t align perfectly with his.

4chan loves remixing Pepe, and also Donald Trump. So the next step was inevitable: an image of Donald Trump as Pepe. Then in October 2015, Trump himself retweeted the image, along with a parody video compilation called "Can’t Stump the Trump" made by Donald Trump fans on 4chan:

At the time, this got almost no attention. Trump was still one of 17 contenders for the Republican nomination, and Pepe was still the most popular meme on Tumblr, not an avatar of the alt-right. A few publications used Trump’s tweet as an entry point to writing about his popularity on 4chan: "Trump’s affiliation with the site might end up hurting the candidate given that racism is virulent on the message board," Vocativ noted, but continued: "It could also help him: Twitter users responded to Trump’s initial twitter post with additional memes offering encouragement."

Trump fans, though, kept tweeting and posting about Pepe. When Politico’s Ben White asked about Pepe in May, he got a barrage of Pepe memes in response, many of them very Trumpy:

What/who is this character and why do I see it associated with Trumpsters/Alt-Right types all the time? pic.twitter.com/BMKXQg6EJy — Ben White (@morningmoneyben) May 16, 2016

The Daily Beast’s Olivia Nuzzi interviewed two anonymous online white supremacists and alt-right movement members who said this kind of collective response was a "campaign to reclaim Pepe from normies." By summer, there were plenty of "normies" out there — political journalists, for example — who weren’t hanging out on 4chan in 2008 or reblogging memes on Tumblr in 2015, and whose first exposure to Pepe was as a symbol used primarily by white supremacists and alt-right Trump supporters.

That’s left people more familiar with the meme’s context scrambling to explain the nuance. "Pepe the Frog is not a Nazi, no matter what the alt-right says," read a headline at the Daily Dot: "He’s not a white supremacist, and he’s not a Trump voter. Hell, he's not even real. He is only what we make him, and in this election, the alt-right is trying to make him theirs."

Does a Pepe meme mean you’re a white supremacist?

Trump himself hasn’t addressed the Pepe controversy. His son Donald Jr. said on Good Morning America: "I've never even heard of Pepe the Frog. I mean, bet you 90 percent of your viewers have never heard of Pepe the Frog. … I thought it was a frog in a wig. I thought it was funny."

But the "Deplorables" meme wasn’t the only time recently that Donald Trump Jr. has seemed to nod to white supremacists. He referenced "warming up the gas chamber" in a recent interview (later saying he was talking about "corporal punishment"), he retweeted a white supremacist, and he appeared on a radio show with a white supremacist who has praised slavery. His tweet comparing Syrian refugees to Skittles was widely criticized but backed by the campaign.

There’s a case to be made that thinking this deeply about Pepe memes plays directly into the trolls’ hands: What trolls, whether Gamergaters, Trump supporters, or both, want is to get a rise out of the audience, and to get attention. With Pepe, they’ve likely succeeded beyond their wildest dreams, even if they represent a tiny fraction of the electorate — and even if they’re in it to troll, not to vote. As Jesse Singal wrote for New York magazine:

The fact that a subset of louder-than-their numbers hyperactive Twitter and image-board users have conscripted the frog for their offensive purposes doesn’t actually mean all that much. It isn’t any more "horrifying" than the fact that there are so many people passing around Nazi imagery online in the first place. This is just how internet culture works, whether the culture in question is an innocent Tumblr fan community or an offense-loving chan subset. It iterates and comes up with new weird ways to communicate information.

The counterpoint is that while internet trolls have always existed, they’re usually something an ordinary campaign would desperately avoid. The Trump campaign, on the other hand, doesn’t care whom it’s empowering. The only reason most of us are even aware of an obscure political meme from 4chan is that Trump promoted it in the first place, way back in October.

This was a choice. It’s not as if Trump is the only cultural figure the alt-righters of 4chan have claimed as their own. They’re also very fond of Taylor Swift, whom they see as their "Aryan goddess." But Swift’s reputation has not suffered, because she doesn’t retweet praise from white supremacists. The reason Trump’s campaign has become associated with racists, xenophobes, and the alt-right is that he’s stood by and let it happen.