Via FAS – Domestic Terrorism: An Overview, Jerome P. Bjelopera, Specialist in Organized Crime and Terrorism. August 21, 2017.
“The emphasis of counter terrorism policy in the United States since Al Qaeda’s attacks of September 11, 2001 (9/11) has been on jihadist terrorism. However, in the last decade, domestic terrorists—people who commit crimes within the homeland and draw inspiration from U.S.-based extremist ideologies and movements—have killed American citizens and damaged property across the country. Not all of these criminals have been prosecuted under federal terrorism statutes, which does not imply that domestic terrorists are taken any less seriously than other terrorists. The Department of Justice (DOJ) and the Federal Bureau of Investigation (FBI) do not officially designate domestic terrorist organizations, but they have openly delineated domestic terrorist “threats.” These include individuals who commit crimes in the name of ideologies supporting animal rights, environmental rights, anarchism, white supremacy, anti-government ideals, black separatism, and beliefs about abortion. The boundary between constitutionally protected legitimate protest and domestic terrorist activity has received public attention. This boundary is highlighted by a number of criminal cases involving supporters of animal rights—one area in which specific legislation related to domestic terrorism has been crafted. The Animal Enterprise Terrorism Act (P.L. 109-374) expands the federal government’s legal authority to combat animal rights extremists who engage in criminal activity. Signed into law in November 2006, it amended the Animal Enterprise Protection Act of 1992 (P.L. 102-346). This report is intended as a primer on the issue, and four discussion topics in it may help explain domestic terrorism’s relevance for policymakers:

• Level of Activity. Domestic terrorists have been responsible for orchestrating numerous incidents since 9/11.
• Use of Nontraditional Tactics. A large number of domestic terrorists do not necessarily use tactics such as suicide bombings or airplane hijackings. They have been known to engage in activities such as vandalism, trespassing, and tax
  fraud, for example.
• Exploitation of the Internet. Domestic terrorists—much like their jihadist analogues—are often Internet and social-media savvy and use such platforms to share ideas and as resources for their operations.
• Decentralized Nature of the Threat. Many domestic terrorists rely on the concept of leaderless resistance. This involves two levels of activity. On an operational level, militant, underground, ideologically motivated cells or individuals engage in illegal activity without any participation in or direction from an organization that maintains traditional leadership positions and membership rosters. On another level, the above-ground public face (the “political wing”) of a domestic terrorist movement may focus on propaganda and the dissemination of ideology—engaging in protected speech…”