Editor's note: Brian Levin is a professor of criminal justice and director of the nonpartisan Center for the Study of Hate & Extremism at California State University, San Bernardino. Levin, a former New York City police officer, is a graduate of Stanford Law School. The opinions expressed in this commentary are solely those of the author.
(CNN) -- The horrendous ambush assassination of two Las Vegas police officers at a pizzeria and the killing of a good Samaritan by a violent young married couple with anti-government hatred again show that domestic extremists on the fringes remain a continuing threat in America.
In fact, in recent weeks the Department of Justice reconstituted a law enforcement working group devoted to addressing right-wing extremism.
One of Sunday's killers, who was reportedly removed by other militia protesters from the Bundy ranch standoff earlier this spring, draped an officer's body with a yellow Gadsden "Don't Tread on Me Flag," a swastika and a note about "revolution."
In the 1970s, a significant violent threat came from small, tight-knit groups of the "revolutionary left" such as the Weather Underground and Symbionese Liberation Army as well as the anti-police Black Liberation Army whose assassination sprees left 13 officers dead across the nation.
Since the early 1980s, however, the domestic extremism threat pendulum has swung right, not only to white supremacists, but to anti-government "Patriot" adherents who sometimes, but not always, embrace hard-core racial prejudice and violence.
Today, according to the Southern Poverty Law Center, these groups number more than 1,000. The left-wing extremist groups of the 1970s operated as small, yet highly structured, segregated offshoots of the nonviolent civil rights and anti-war community.
Unlike the more consistently planned bombings and premeditated assassinations of the 1970s left, right-wing violence today runs the gamut from Sunday's ambush to more spontaneous killings that follow car stops or police calls about relatively mundane disputes. In 2010, two West Memphis, Arkansas, police officers were killed by anti-government extremists during a routine car stop, and in 2009 three Pittsburgh officers died during a domestic disturbance call at the home of a gun-obsessed neo-Nazi.
Today's violent right-wing extremists often operate on the fringes of existing groups or social networks, where they gain inspiration and a belief system in lieu of directives or an actual rank or "membership" card. While many of these favored groups are extremist, some are not.
Jerad Milller, who police said carried out the Las Vegas attack with his wife, Amanda, reportedly went to the Bundy ranch militia protests and even posted a picture of a meeting he had with an extremist conspiracist on his Web page. He also used a flag popular with the right at the crime scene and "liked" various mainstream political groups such as the National Rifle Association, whose executive vice president called federal agents "jack-booted thugs" during the heyday of the 1990s militia movement, on his Facebook page. His posted manifesto contains overheated versions of themes that could fit into a mainstream political speech, with its vow to fight tyranny.
To be sure, mainstream groups in politics countenance reform, not murder, but the often-shrill rhetoric, conspiracy theories and innuendo they sometimes promote may have consequences. Alex Jones, a popular radio personality of the far right, went so far as to accuse the federal government of staging the Las Vegas incident for political gain.
Members of law enforcement are among the most visible and active civic officials to interact directly with the public, so their symbolism and proximity make them targets for those who hate and loathe the government. Moreover, many police interactions involve emotionally tense situations, making law enforcement susceptible not only to premeditated violence but spontaneous attacks as well.
Extremists, unlike political players, have opted out of accepting the peaceful processes and institutions of our pluralistic democracy. The Las Vegas killers had not only targeted officers as a tyrannical enemy but may have planned an attack on a courthouse as well.
When we engage in political debate, we have to be mindful that the embers of dissatisfaction with government can fly and land on violent and sometimes unstable people who rely on conspiracy theories as an anesthetic for either personal failures or emotional frustrations.