06/10/2014 08:57 am ET Updated Aug 10, 2014

What Drives Anti-Government Extremists

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...

Please see CNN's opinion page, who kindly allowed for this partial repost, for the remainder of this OpEd.

Note: Professor Brian Levin, a former NYPD officer and Stanford Law graduate has testified before Congress on right wing extremism and has advised federal and local authorities for over two decades. He is co-author of The Limits of Dissent, and is director of California State University San Bernardino's Center for the Study of Hate & Extremism.