On Saturday, a few hours after eleven people were murdered at the Tree of Life synagogue in Pittsburgh, I put on a tuxedo and went to my cousin’s wedding. The ceremony was brief and buoyant. When it was over, a few relatives and I stood around the raw bar—yes, it was the kind of semi-Jewish wedding that has a raw bar—exchanging anecdotes about the happy couple. The news of the day came up once or twice, but, really, what was there to say? The killing was horrible, senseless. It defied all logic. I had a pedantic quibble with this, although, in the moment, I kept it to myself. The shooting was an egregious act of hatred, of course; and yet it did, strictly speaking, follow a twisted kind of logic.

Robert Bowers, the suspect in the Pittsburgh shooting, had an account on Gab, the “free speech” social network rife with hate speech, which has since been taken down. “There is no #MAGA as long as there is a kike infestation,” he wrote, a few days ago, using the acronym for Make America Great Again. A few days before that, he posted a link to a YouTube video called “The Mass Migration Agenda,” along with the message “diversity for you but not for jew.” He also posted various images of cackling Jewish caricatures, Holocaust-denialist memes, and a sign reading “Gas the Jews.” To the uninitiated, this all seems like blind, blithering hatred. In fact, it’s part of a pernicious yet internally consistent world view. It should go without saying that Bowers’s world view is wrong, both morally and empirically. (That this doesn’t go without saying is just one of the numbingly dystopian facets of life in 2018.) And yet it’s worth trying to parse the logic, if only to understand where we are and how we got here.

In 2016, when I started tracking the online cohort of bigots, trolls, and nihilists that was coming to be known as the alt-right, I didn’t expect to find much overt anti-Semitism. Transphobia, misogyny, the invocation of the invading horde in the person of Syrian refugees—that much I anticipated. But hoary tropes about Jewish bankers and Zionist-occupied government? Those seemed like something out of the nineteen-thirties—or, for that matter, like something out of the zero-thirties, the decade when the Jews were first accused of killing Christ. Hadn’t the extremists evolved since then?

Well, yes and no. After spending just a few hours on certain corners of Reddit and 4chan and Gab, it became clear that I would have to reacquaint myself with “Mein Kampf” and “The Protocols of the Elders of Zion.” And I soon learned that there were newer texts I’d have to read. Last year, when I was reporting a piece about a bilious anti-Semite who co-hosted a podcast called “The Daily Shoah,” I looked for the turning points in his thinking—the moments when his casual racism and his contrarian distaste for progressive piety congealed into a single ethos, one premised on categorical anti-Semitism. The main such turning point happened after he read “The Culture of Critique,” a book by a psychology professor named Kevin MacDonald. Published in 1998, the book is a cornerstone of a good amount of neo-fascist discourse online. I ordered the book on Amazon and forced myself to read it. Then I had to grapple with the ethical question of whether to rebut each of MacDonald’s shoddy arguments, or whether paying any attention to him, even negative attention, would only continue to fuel his viral success—another very 2018 dilemma.

I decided that MacDonald’s ideas, even the most specious ones, were too influential to ignore. He calls himself an evolutionary psychologist, and he believes that the best way to understand Judaism is not as a religion but as a “group evolutionary strategy.” Over millennia, he argues, Jews have developed certain traits: high verbal intelligence, ambition, loyalty to insiders, wariness of outsiders; and a fierce instinct for self-preservation, even at the expense of their host society. “The main thrusts of Jewish activism against European ethnic and cultural hegemony,” MacDonald wrote in a preface to the 2002 edition of the book, “have focused on three critical power centers in the United States: The academic world of information in the social sciences and humanities, the political world where public policy on immigration and other ethnic issues is decided, and the mass media.” Many of MacDonald’s readers on the extremist Internet follow his argument to a more pointed conclusion: that the Jews are the single greatest threat to white power in America. (It’s a tenet of alt-right dogma that Jews are not white.) For a while, MacDonald tried to dissociate himself from the white supremacists who use his work as a justification for their more overt bigotry. He isn’t doing so anymore.

“The Culture of Critique” remains a key text within the anti-Semitic alt-right, and many online neo-fascists—such as the proprietors of the Daily Stormer, who refer to MacDonald, with affection, as K-Mac—continue to expand on his arguments. According to this line of thinking, the Jewish agenda is, at its core, a pro-immigration agenda, with the ultimate goal of decoupling the U.S. from its history as a majority-white nation; Jewish advocacy for multiculturalism is yet another attempt, whether conscious or unconscious, at Jewish self-preservation. A cohesive white majority might expel the Jewish nuisance from their midst, as so many nations have done in the past; therefore, it’s in Jews’ collective interest to keep white Americans divided, allowing a coalition of ethnic minorities, Jews among them, to take power. And, on the most racist parts of the Internet, the end of white hegemony is routinely equated with the downfall of America.

MacDonald is now a retired academic. (In 2008, the academic senate of California State University, Long Beach, where he was a tenured professor, issued a statement saying that it “unequivocally disassociates itself” from his views.) He is not a militia leader, and he does not endorse violence. It’s not evident that Bowers had any firsthand knowledge of “The Culture of Critique”; if he committed this atrocity, then his actions are his alone. It is clear, however, that the bad ideas in that book have contributed to a festering online ecosystem of even worse ideas, and that Bowers seems to have been warped by that ecosystem. Last week, on Gab, he reposted a meme: “Jews are waging a propaganda war against Western civilization . . .You are living in a critical time in history where the internet has given us a small window of opportunity to snap our people out of their brainwash.” Not all reposts are endorsements, but Bowers seemed to agree with the sentiment. Just a few moments before the shooting, he posted his last message on Gab. He did not use the measured rhetoric of an academic or the goading tone of a troll; rather, he sounded like a man suffering from the all-encompassing delusion of persecution, one who has been convinced that terrorism is actually heroism. “HIAS”—the Hebrew Immigrant Aid Society, a refugee-resettlement group—“likes to bring invaders in that kill our people,” he wrote. “Screw your optics, I’m going in.”