Leon Czolgosz was an anarchist who shot and killed William McKinley, the twenty-fifth president of the United States. Czolgosz, who had emigrated from Poland, believed that McKinley was an enemy of working people. His action put Theodore Roosevelt in the White House, and it also highlighted the ominously violent image of anarchism.

The beginning of the twentieth century was a time of rapid societal changes. Anarchism, the belief that people should not be ruled by organized government, caught on among the poor and the working class. Some anarchists advocated more radical views than others, and Czolgosz belonged to this camp.

The son of Polish immigrants, Czolgosz grew up in poverty, and he grew into a bitter adult. (During his trial he made no secret of his hatred for the United States.) He eventually settled in the New York town of West Seneca. There he quickly established a reputation...