Harking back to The Authoritarian Personality, a 1950 study of the personality traits that make someone susceptible to authoritarian rule, this volume joins the growing library of attempts to understand supporters of U.S. President Donald Trump. Hibbing draws on focus groups and extensive surveys to argue that such individuals differ from their counterparts in the 1950s. They are not searching for an all-powerful authority figure; instead, they feel a mission to protect their families and culture from an expansive, shifting group of “outsiders.” In the Trump era, these grew to include religious minorities, immigrants, supposed welfare cheats, athletes who knelt during the national anthem, and, more broadly, non-Americans and nonwhites. Hibbing dubs these avid Trump supporters “securitarian personalities,” who don’t fear external attack so much as this unending flow of domestic threats. They see the world not as “us versus them” but as the even more sweeping “us versus not-us.” The purpose of Hibbing’s inquiry is undeniably important, since Trump’s voter base will long outlast him. But as with so many other efforts to comprehend Trump’s base, Hibbing sheds some light without providing a fully satisfying set of answers.