From the Executive Summary: "This report outlines ongoing work by the Department of Defense to address the threat posed by prohibited extremist activities. The Department of Defense has long prohibited Service members from actively engaging in extremist activities. Since 1969, the Department of Defense has provided policy guidance that enumerates the prohibition of specific activities, and has routinely updated its guidance to clarify prohibited activities, clarify the investigative authorities that commanders have at their disposal, and ensure that all military departments implement training on these policies. Following a number of high-profile insider threat attacks in the early 2010s, the Department of Defense built a program to detect, deter, and mitigate such threats to the Department, its people, and its mission. In 2019, Congress directed the Department of Defense to review existing policies and capabilities with the aim of closing gaps in personnel security vetting. In 2020, the Army published a comprehensive revision of Army Command Policy (AR 600-20) which was the first of its kind to address the use of social media to support extremist activities and provided guidance to commanders for addressing prohibited activity that crosses the line into misconduct."
United States Department of Defense: https://www.defense.gov/