The term 'salad bar' extremism, and others like it, refer to 'idiosyncratic patterns of radicalization,' one expert said.
John Cohen, a former U.S. Department of Homeland Security acting undersecretary for intelligence and ABC News contributor, points to several factors that are contributing to this phenomenon in the U.S., including a highly-polarized society in which some people feel that violence is acceptable, and an online and media environment that is "saturated" with extremist content.
"We as a people are becoming more incoherent," he said. "Extremists are becoming more incoherent as well."Such extremists may pop up on law enforcement's radar prior to attacks -- such as a concerned call from a family member -- but the U.S. lacks a "cohesive strategy" in the investigation and prevention of this threat, according to Cohen.
"We understand where jihadist groups exist, we can see very concretely what the neo-Nazi white supremacist sphere is," Gartenstein-Ross said. "For idiosyncratic, violent extremism, what's the digital or real-world community that forms a part of the extremist's milieu?" "We have to employ not just traditional law enforcement strategies to address it, but also community-based threat management strategies that involve collaborative efforts involving mental health professionals, law enforcement, community groups, faith leaders," he said.