From the Executive Summary: "Preventing terrorist attacks remains a top priority for both the FBI and the Department of Homeland Security (DHS). The threat posed by international and domestic threat actors has evolved significantly since 9/11. The greatest terrorism threat to the Homeland we face today is posed by lone offenders, often radicalized online, who look to attack soft targets with easily accessible weapons. Many of these violent extremists are motivated and inspired by a mix of socio-political goals and personal grievances against their targets. With this report, we are providing our strategic intelligence assessments on DT [domestic terrorism], a detailed discussion of our procedures and methods to address DT threats, as well as data on DT incidents and our investigations."
Office of the Director of National Intelligence: https://www.dni.gov/