Running through President Trump’s scattered response to the most recent mass shootings, with its vague gestures toward the evils of the internet and video gaming, and the brief hostage video in which he formally renounced racism, the concept that kept recurring was mental illness. Trump returned to the killers as “disturbed minds,” proposed to “better identify mentally disturbed individuals who may commit acts of violence” through unspecified means, and declared, “Mental illness and hatred pulls the trigger, not the gun.”

Here, Trump was repeating a trope that emerged over the weekend, and which he and his defenders have used to deny the ideological link between the El Paso shooter and his own administration. “If you look at both of these cases, this is mental illness. These are peop … really, people that are very, very seriously mentally ill,” Trump said last night. “This was a sick person,” said White House chief of staff Mick Mulvaney, in one interview. “No politician is to blame for that.” In another interview, Mulvaney dismissed the killers as “crazy people, sick people.”

Mental illness is the concept Republicans have grasped onto to absolve Trump and his allies of any ideological kinship with white nationalist terrorists. “Crazy” is a kind of metaphysical demarcation between conservatism and terrorism. If you think about this very carefully, however, it is not much of a defense at all.

Sometimes gunmen do target politicians for reasons that have no real connection to established ideology. The man who shot Gabby Giffords a decade ago was just crazy, and I wrote a piece at the time pushing back against the somewhat popular accusation that his attack somehow implicated the tea party. What’s more, it’s also true that white nationalists such as the El Paso shooter have more extreme beliefs than Trump, and their methods are distinct from, and probably at odds with, Trump’s strategy.

White nationalist terrorism and Trump-style conservatism both lie along a continuum of thought. Both share the crucial belief that immigration from Mexico poses an existential threat to American society requiring radical and violent response. Trump has used lurid depictions of crime committed by unauthorized immigrants to stoke fear. (“We cannot let this butchery happen in America.”)

Even as long as a decade ago, Republicans felt enough kinship with white nationalists that they objected to efforts by Homeland Security officials to monitor and neutralize it as a threat. Daryl Johnson, a former analyst at the department, recounted the firestorm that ensued when he identified “right-wing extremism” as a domestic-terror threat. That defensiveness has increased as Trump has drawn white nationalists closer to the party. A former FBI agent tells the Washington Post, “There’s some reluctance among agents to bring forth an investigation that targets what the president perceives as his base.”

And Trump himself, in a chilling morning tweet, confirmed his assumption that white nationalist terrorists are, at least loosely speaking, on his side. “Fake News has contributed greatly to the anger and rage that has built up over many years,” he wrote. “News coverage has got to start being fair, balanced and unbiased, or these terrible problems will only get worse!” Trump’s own formulation depicted the killer as punishing Trump’s enemies, carrying out the president’s own impulses — in a more extreme fashion than he would prefer, certainly, but acting out of sympathetic and shared motives.

The main problem with the distinction between right-wing politics and mental illness is that it is impossible to tell where one ends and the other begins. There are obviously many sane and even cogent elements to conservatism. But the conservative movement has always included paranoid elements. Richard Hofstadter’s classic analysis of “the paranoid style” used Joe McCarthy, the John Birch Society, Phyllis Schlafly, and other central figures in conservative movement as its primary subject.

Hofstadter was careful to note that he used the term “paranoid” in the metaphorical sense, not as a clinical diagnosis. But the modes of thought he analyzed, which charged a vast secret communist conspiracy had gained control of the U.S. government, were not notably more cogent than the recent manifestos circulated by white supremacist shooters. The takeover of the Republican Party by right-wing paranoids is a decades-long trend that Trump has both benefited from and accelerated.

Tim Alberta’s new book, American Carnage, reports a secret 2013 meeting between John Boehner and Roger Ailes, then the chairman of Fox News. Boehner was concerned that Fox had been giving too much airtime to the loopiest conspiracy-mongers in his caucus, like Louie Gohmert, Steve King, and Michele Bachmann. He asked Ailes to reduce their exposure, and offered up a concession in return: Boehner was promising another committee to investigate Benghazi. The mere mention of Benghazi “tripped a switch,” Alberta reports. “Suddenly high-strung and wary of his surroundings, Ailes proceeded to unpack for Boehner the outlines of an elaborate, interconnected plot to take him down. It started with Ailes’ belief that Obama really was a Muslim who really had been born outside the United States. He described how the White House was monitoring him around the clock because of these views.” Bohener told Alberta, “I began to realize that Ailes believed in all this crazy stuff.”

One of the conclusions that can be drawn from this story is that paranoid thinking had permeated the GOP even before Trump conquered the party. It was Marco Rubio, standard-bearer for the party’s mainstream wing, who charged that President Obama had “deliberately weakened America.” Ailes of course was not some backbencher or marginal crank, but the director of the most influential news organization in the United States. And while Alberta doesn’t point this out, it’s worth pausing to note that Boehner’s position — that yet more investigation was needed to get to the truth behind Benghazi — was also a conspiracy theory. Both men in the room were chasing unfounded conspiracy theories, and the difference between their levels of paranoia was merely a matter of degree.

Trump’s allies may think it constitutes some kind of defense to dismiss his white nationalist allies as crazy. In truth, it reveals something much more damaging about themselves.