From 1910 to the end of World War I, American society witnessed a tremendous outpouring of books, pamphlets, and especially newspapers espousing virulently anti-Catholic themes and calling on readers to recognize the danger of Catholicism to the American republic. By 1915 the most popular anti-Catholic newspaper, The Menace, boasted over 1.6 million weekly readers. Justin Nordstrom's Danger on the Doorstep examines for the first time the rise and abrupt decline of anti-Catholic literature during the Progressive Era, as well as the issues and motivations that informed anti-Catholic writers and their "Romanist" opponents. Nordstrom explores the connection between anti-Catholicism and nationalism from 1910-1919. He argues that the anti-Catholic literature that occupied such a prominent place in the cultural landscape derived its popularity by infusing long-standing anti-Catholic traditions with the emerging themes of progressivism, masculinity, and nationalism. Nordstrom demonstrates that in the pages of anti-Catholic texts, Catholicism emerged as a manifestation of and a scapegoat for the dangers of modernity--including rampant urbanization, immigration, political corruption, and the proliferation of power conglomerates. Samples of Menace cartoons underscore Nordstrom's arguments. This fascinating look at an understudied episode of anti-Catholic radicalism will be of interest to scholars and students of religious history, popular culture, and journalism.