“If they did the same thing that they did with the Muslims, they’d say every white guy is a potential terrorist,” said Martin R. Stolar, a New York civil rights lawyer. “You can’t do that with white people. The blowback would be outrageous.”
The rise in the white supremacist threat has paralleled an increasing racialization and divisiveness in the nation’s immigration debate. Mr. Trump has used ethnonationalist language that his opponents argue is arousing political extremists. Even in past years, some political leaders have been slow to recognize the existence of domestic terrorism: After the Oklahoma City bombing, Newt Gingrich, at the time the speaker of the House, refused to hold hearings on white nationalist terrorism.
In the years since, the nature of white supremacism has changed. It used to be that white supremacists, for the most part, operated in groups, often living in the same area, said Brian H. Levin, director of the Center for the Study of Hate and Extremism. The chapters had some control over the timing and choice of targets. He cited as examples Aryan Nations, the Ku Klux Klan and local Nazi skinhead groups.
“The top-down hierarchies of the past have been increasingly supplanted by a more democratized and a geographically dispersed set of erratic do-it-yourselfers,” he said. “Now, so-called lone wolves are turbocharged by a fragmented and hate-filled dark web which has become a modern-day, virtual neo-Nazi boot camp available 24-7 anywhere in the world with an internet connection.”
Examples of these kinds of actors are the attackers in the Poway synagogue shooting, the mass shooting at a synagogue in Pittsburgh last fall and now, according to the authorities, El Paso.
While these men often act alone, the F.B.I. says that technology has allowed American terrorists to plug into a global community of terrorists who espouse similarly hateful ideologies. Domestic terrorists are increasingly citing terrorists overseas in their killings. In his manifesto, the suspected El Paso gunman said that he agreed with the terrorists who attacked two mosques in Christchurch, New Zealand. Those killers in New Zealand said in their manifesto that they had been inspired by Dylann Roof, who murdered nine people at the Emanuel African Methodist Episcopal Church in Charleston, S.C.
Ali Soufan, a former F.B.I. special agent and the author of “Anatomy of Terror,” said he had been struck by how much white supremacists resemble the jihadis he spent so many years fighting.