Troubled Loner or Radical Recruit? In Political Violence, It’s Often Hard to Say

The search for a larger lesson in the invasion of House Speaker Nancy Pelosi’s home, chiefly from among the details of the accused invader’s life and social media history, have, like so many things in American life, split by partisanship.

“The Republican Party and its mouthpieces now regularly spread hate and deranged conspiracy theories,” Hillary Clinton, the 2016 Democratic presidential nominee, tweeted. “It is shocking, but not surprising, that violence is the result.”

Or, arguing that politics were secondary in the attack — which left Ms. Pelosi’s husband, Paul Pelosi, badly injured — Howard Kurtz of Fox News wrote, “With a defendant so obviously mentally disturbed, who cares what his ideological views are, other than that he planned to kill Nancy Pelosi?”

Just because a debate is partisan does not mean that both views are equally valid. Experts in political violence have argued for years that dehumanizing and apocalyptic language by prominent right-wing figures is helping to drive the rise in far-right violence. Federal agencies call far-right terrorism a growing threat.

And then there is this: Notions that Mr. Pelosi’s attacker may have been inspired by acrimonious political messaging are not so in tension with the idea that the assailant may be a troubled loner who latched onto political conspiracies incidentally.

Some extremism researchers see those two motivators as so intertwined that there is even a name for the sort of violence they can jointly provoke: stochastic terrorism.

Stochastic terrorism is defined as violence committed by an attacker who, though acting on personal volition, is inspired by language demonizing the target. It has existed for as long as hatemongers have urged their communities to despise some racial or religious minority in their midst.

What details have emerged about David DePape, the man accused of attacking Mr. Pelosi, have raised the possibility that his attack might fit this model. Prosecutors’ filings portray him as acting on behalf of right-wing political narratives that characterized Ms. Pelosi as a danger to the nation. But the filings also give no indication that the attack was anything other than his idea alone.

Other details about Mr. DePape suggest that he was adrift and emotionally troubled. This is hardly unusual with individuals who commit violence on behalf of some cause encountered online — indeed, it is a profile that extremist groups are known to actively pursue — but it makes the question of motivation a psychological as much as a political one.

The term “stochastic terror” emerged in the 2010s, as extremist groups of all stripes began using the internet to reach millions in the hopes that even one individual might be inspired to action. It comes from the Greek word stochastikos, meaning randomly determined or a guessing aim, referring to the instigators’ inability to control who will act on their incitement or how.

The messiness of assigning motive in such cases means that society’s biases can sometimes intrude. In the United States, white attackers are often identified as disturbed loners, where a Muslim attacker with a similar profile might more readily be called a terrorist, for example.

What we now call stochastic terror is most associated with modern jihadist groups like the Islamic State, which have issued online calls for volunteers to indiscriminately attack civilians in countries at war with the groups.

But they did not invent such methods. In the early 1900s, Russian newspapers filled with hateful conspiracies against Jews, helping to provoke the waves of communal violence known as pogroms. In the 1960s in the United States, a series of angry loners acted on far-right language demonizing civil rights leaders, launching a wave of assassinations.

More recently, in India, Hindu nationalist groups have trumped up accusations against the country’s Muslim minority, inspiring some Hindus to turn on their Muslim neighbors.

Often, the demonizing language might inspire violence without calling for it explicitly. Instead it suggests that the offending target poses a danger so grave that extreme action may be necessary.

In a paper last year, Molly Amman, a former profiler for the F.B.I., and J. Reid Meloy, a forensic psychologist, cited as one example an attempted plot to kidnap and perhaps kill Gretchen Whitmer, the governor of Michigan.

The accused plotters appeared to be likely acting in part, the authors suggested, on language from then-president Donald J. Trump portraying Ms. Whitmer as a runaway despot and urging followers to “liberate Michigan.”

That there was no explicit link between Mr. Trump’s language and the accused plotters’ actions, and that Mr. Trump may not have even intended as much, can be typical of such violence, Ms. Amman and Mr. Meloy argued.

“The speaker’s rhetoric may range from bombastic declarations that the target is a threat by some measure, to ‘jokes’ about violent solutions, or to the shared problem posed by the target,” the authors wrote.

In individual cases, the authors added, the speakers’ intentions are often impossible to prove, as is the role of that speech in nudging some listener closer to action.

Sometimes this is deliberate, meant to instigate violence while inoculating the speaker from blame. But sometimes the language is not aimed at incitement at all, but merely at rallying supporters in ways that provoke some of them to action.

But, regardless of intent, the instigating speech tends to follow a pattern far more specific than merely denigrating some individual or group — meaning that, like calling “fire” in a public theater, the resulting danger is foreseeable.

Messages in these cases tend to divide the world between a pure and virtuous “us,” who is besieged by an implacably hostile “them.” Listeners are told that they are locked in an existential battle with enemies who seek their total domination and the destruction of their way of life.

This threat is portrayed as imminent and unchecked — justifying, even necessitating, drastic steps to prevent it. And the speaker often describes society as having fallen into lawlessness and chaos, leading some listeners to conclude that they alone have the power to act.

J.M. Berger, a scholar of extremist violence, has called this “the crisis-solution construct,” writing that it can resonate especially with isolated or troubled individuals. It reframes their personal struggles as caused not by impersonal social or economic forces, but by the nefarious actions of some “them” group waging a war on the listener’s virtuous “us” group.

This makes the listeners feel less alone, their hardships feel more comprehensible and the solution, however extreme, within their power to impose.

Some argue that the motivation of such attackers, on an individual level, could be said to be chiefly psychological, the details of whatever political cause they latched onto almost incidental.

“The connections between mental illness, conspiratorial thinking, right-wing rhetoric, and violence are made in our heads, not theirs,” the writer Jay Caspian King wrote in an essay for The New Yorker on efforts to understand Mr. DePape.

“How we ultimately choose to describe these violent men often betrays more about us than about them,” he added.

But such a view misses the point of how stochastic terrorism works, scholars have argued.

As political demonization following the script of incitement saturates a society, regardless of whether the propagators of that language intend as much, the odds that someone will follow through on the implied call to action increases sharply.

If those people are often lost souls with histories of unruly behavior who appear to have only a tenuous relationship to the political causes that seemed to help inspire them, then this is how extremist recruitment has always worked.

The propensity of such language to provoke violence is established enough that some terrorist monitoring groups now track upticks in such speech as an early-warning indicator for attacks that are thought to follow as a result.

Sure enough, as extremist right-wing language has escalated across Western countries in recent years, so have attacks by white extremists, many of them seemingly loners.

Ms. Amman and Mr. Meloy, the extremism researchers, warned that the diffuse nature of this threat, emerging as it can from individuals with no formal ties to hate groups, makes it both especially dangerous and devilishly difficult to prevent.

“It is as dire as it sounds,” they wrote.