Most Republicans in a January 2020 survey agreed that "the traditional American way of life is disappearing so fast that we may have to use force to save it." More than 40% agreed that "a time will come when patriotic Americans have to take the law into their own hands." (In both cases, most of the rest said they were unsure; only one in four or five disagreed.) I use 127 survey items to measure six potential bases of these and other antidemocratic sentiments: partisan affect, enthusiasm for President Trump, political cynicism, economic conservatism, cultural conservatism, and ethnic antagonism. The strongest predictor by far, for the Republican rank-and-file as a whole and for a variety of subgroups defined by education, locale, sex, and political attitudes, is ethnic antagonism-especially concerns about the political power and claims on government resources of immigrants, African-Americans, and Latinos. The corrosive impact of ethnic antagonism on Republicans' commitment to democracy underlines the significance of ethnic conflict in contemporary US politics.