The El Paso manifesto, if it is verified, ties the attacker into the mainstream of the white power movement, which came together after the Vietnam War and united Klan, neo-Nazi, skinhead and other activists. That movement, comparable in size to the much better known John Birch Society, never faced a major prosecution or crackdown that hobbled its activity. As a result, it was able to sink deep roots into society, largely under the radar of most Americans.

This movement is often called white nationalist, but too many people misunderstand that moniker as simply overzealous patriotism, or as promoting whiteness within the nation. But the nation at the heart of white nationalism is not the United States. It is the Aryan nation, imagined as a transnational white polity with interests fundamentally opposed to the United States and, for many activists, bent on the overthrow of the federal government.

The white power movement imagines race war, incited by mass violence among other strategies. The core texts of this movement, like “The Turner Diaries” or “Camp of the Saints,” aren’t just quaint novels, but rather provide a road map to how such violence could succeed. To call them manuals is too simplistic: They provide the collective ideas and vision by which a fringe movement can attempt a violent confrontation that could lead to race war.

These ideas run from the earlier period directly into today’s manifestos. Dylann Roof’s document discussed his desire to provoke race war. The Christchurch manifesto used images and phrases from the earlier movement. In the El Paso manifesto, the anti-immigrant rhetoric is thoroughly ensconced in other white power ideas.

To be sure, mass attackers today have a new set of coded phrases, such as “replacement,” as a code for racial annihilation through intermarriage, immigration and demographic change. But the idea of that threat has been central to white power activism for decades.

To people in this movement, the impending demographic change understood by many commentators as a soft transformation — the moment when a town, a county, or a nation will no longer be majority-white — isn’t soft at all, but rather represents an apocalyptic threat.

As horrible as the El Paso attack was, this movement is capable of even larger-scale violence. The Oklahoma City bombing, its most horrific act to date, was the largest mass murder on American soil between Pearl Harbor and 9/11. Not only do we still lack a widespread understanding of that bombing as an act of political violence, but we fail to reckon with the many activists that create shrines to Timothy McVeigh and hope to follow in his footsteps.

It is not enough to dismiss mass shootings as horror beyond our comprehension. It is our duty to understand their meaning and confront the movement that relies upon them.