Neither ISIS nor al-Qaeda is yet vanquished either, and they remain priorities for the department despite efforts to pay more attention to other ideological actors, and even violence motivated by no ideology in particular, such as the Sandy Hook school shooting. McAleenan noted the problem of people returning to the U.S. after fighting in Syria, and said the department can’t lose focus on what he says has worked in the past against jihadist terrorism. “We’ve prevented another 9/11,” he said.

DHS is now trying to correct gaps in its understanding of terrorist threats, calling for, among other things, an annual report “evaluating the domestic threat environment.” This is important, Selim said, but the fact that no such report yet exists shows that the government is already behind. “We’ve lost significant time that could have been devoted to studying the behavioral and social issues that motivate domestic violent extremists.”

The problem of extremist violence, no matter the ideology, is also one that runs up against the first two amendments of the U.S. Constitution. Communications technologies can help connect extremists in communities, where they encourage and feed off one another, even inspiring or facilitating the planning of attacks. Guns are easy to get and hard to regulate. Preventing violence often involves trying to predict it—and right up to the moment of an attack, any “warning sign,” such as a racist social-media post, can just as easily be a false positive. That’s assuming such a sign comes in time to do anything about it; the El Paso attacker posted his manifesto about 18 minutes before he started shooting.

And as the document acknowledges, holding extremist beliefs is not a crime, so there are limits to what law enforcement can do when it comes to prevention. (As FBI Director Christopher Wray told Congress this summer: “We, the FBI, don’t investigate ideology, no matter how repugnant. When it turns to violence, we’re all over it.”) Hence the document’s emphasis on community partnerships and “off-ramps” such as counseling for people seen as at-risk. The success of such programs will be difficult to measure—how do you count attacks that haven’t happened?

These are all practical challenges that DHS officials are well aware of. There are also political challenges. There is growing bipartisan consensus that right-wing extremism, including white-supremacist violence, is a problem that merits urgent attention. Trump, who was condemned as equivocating about “good people on both sides” after a white-supremacist rally in Charlottesville, Virginia, in which a counterprotester was killed, condemned hatred and bigotry after the El Paso shooting. Trump’s National Security Council for the first time identified nationalist and neo-Nazi groups as a terrorist threat in its own strategy last year. Notably, however, the shooter’s manifesto used the same language the president has in the past used about an “invasion” of immigrants, though it also specified that his views predated the Trump administration.