The sovereign citizen movement is one of the largest antigovernment nationalism or domestic terrorist collectives in the United States. In the last decade, over a dozen public officials were injured or killed by individuals adhering to sovereign citizen ideology. The Terrorist Radicalization Assessment Protocol (TRAP-18; Meloy & Gill, 2016; Meloy, Habermeyer, & Guldimann, 2015) is a collection of 18 behavior-based warning signs for terror incidents which has been used to assess primarily international terrorism samples. In this study, the researchers applied the TRAP-18 to both violent and nonviolent incidents involving sovereign citizen members. Using chi-square tests for independence and a logistic regression analysis, the researchers found support for the TRAP-18. The sum of the TRAP-18 scores was able to postdict violent outcomes within the events included within the study. This important finding should guide future research on the use of the TRAP-18 involving sovereign citizens’ collectives and other domestic groups who exhibit violence. (PsycINFO Database Record (c) 2019 APA, all rights reserved)