At least 49 people were killed at two mosques in Christchurch, New Zealand, on Friday. The suspect who has been arrested in the attacks appears to have decorated the weapons used in the killings with white-supremacist iconography and written online that his acts constitute a defense of the white race and/or “the West” against “Islamic invaders.” The paranoid belief that such a conflict exists, which was once a fringe position in U.S. politics, has become almost commonplace in recent years—largely thanks to Donald Trump, his advisers, and his allies.

In 2014, then-Breitbart publisher Steve Bannon, who’d go on to serve as Trump’s campaign chairman and as a White House adviser, appeared at a Catholic Church–connected conference to discuss what he described as the “very beginning stages of a very brutal and bloody conflict” between “the Judeo-Christian West” and “jihadist Islamic fascism.” Bannon said the threat of ISIS and other global jihadist movements had to be taken in context with “the long history of the Judeo-Christian West[’s] struggle against Islam,” and that “every day that we refuse to look at this as what it is, and the scale of it, and really the viciousness of it, will be a day where you will rue that we didn’t act.” On at least three occasions, Bannon has praised the foresight of a 1973 novel called The Camp of the Saints in which whites in Europe and the U.S. are violently oppressed by invading armies of nonwhite refugees. The (white) author of the novel once said he believed “the proliferation of other races dooms our race, my race, to extinction.”

While Bannon’s 2014 comments arguably implied a distinction between radical and “normal” Islam, the Trump campaign that he joined in August 2016 drew no such lines, repeatedly portraying Muslims in the U.S. as a fifth column. In December 2015, Trump called for “a total and complete shutdown of Muslims entering the United States” after the San Bernardino, California, mass shooting, a call that he reiterated when 49 people were shot and killed at the Pulse nightclub in Orlando, Florida. (The shooter in Orlando was Muslim but had in fact been born on Long Island.) In a speech he gave about the Pulse massacre, Trump criticized Florida and San Bernardino’s “Muslim communities,” asserting (with, it hardly needs to be said, no supporting evidence) that those communities had known in advance that the perpetrators “were bad” but “didn’t turn them in.” Shortly before Bannon became campaign chairman, Trump suggested that Khizr Khan, the Muslim father of an American soldier who died in Iraq, supported terrorism.

After Trump took office, his speechwriter Stephen Miller collaborated with Bannon to create the first version of the so-called “travel ban,” an executive order which shut down travel to the United States from seven majority-Muslim countries on national security grounds. That order was struck down in courts; a revised version of the ban, which is less restrictive and targets non-Muslim countries as well, is still in effect. In 2017, Trump gave a speech in Warsaw in which he asked rhetorically whether “the West” had “the will to survive”—to “protect our borders” and “preserve our civilization” against threats from “the south” that include radical Islam. Miller was reportedly also the driving force behind a Trump push to restrict legal immigration by cutting the number of visas allotted to “shithole” countries in Africa and increasing the number given to “places like Norway.”

Throughout Trump’s campaign and presidency, he and his son Don Jr. have frequently engaged online with enthusiasts of the so-called “alt-right” who espouse the belief that whites are justified in maintaining political dominance by virtue of cultural and/or genetic superiority. This belief is sometimes accompanied by claims that laws and norms which allow for increasing nonwhite populations constitute a slow-motion “white genocide,” a phrase that appears in both the New Zealand shooter’s writing and in the handle of a Twitter user Trump once retweeted. It’s a concept embraced by one of the president’s most outspoken allies in Congress, Iowa Rep. Steve King, who has said that “we can’t restore our civilization with somebody else’s babies” and that “if we don’t defend Western civilization, then we will become subjugated by the people who are the enemies of faith.” King was stripped of his committee assignments in January after he told the New York Times he didn’t understand why it was considered offensive to be a white supremacist, but Trump never criticized the remark.

Trump’s defenders will no doubt argue that every mainstream political belief system has its own extreme offshoots. What makes Trump’s connections to white nationalist attackers unique, however, is that he’s the one who made white nationalism mainstream. Even George W. Bush’s aggressively anti-“terror” administration enforced a distinction between radical and peaceable Islam, and getting caught endorsing racial hierarchies was until recently something that even Republicans had to resign over. Trump took a politically dormant, race-obsessed subculture—one that has been strongly associated, both historically and in recent times, with violence—and demonstrated that its ideas could still support a national figure. He shouldn’t be able to argue that he comes from the respectable, morally acceptable wing of the American nationalist movement, because such a thing doesn’t exist.