Universal theories can have a certain tidy attraction. In science, they can result in revolutionary breakthroughs — Albert Einstein’s Theory of Relativity comes to mind. In the messy realm of human affairs, however, universal theories have a tendency to fall apart. Ruy Teixeira, of the leftist Center for American Progress, provides a textbook example of a brilliant man developing a theory for determining the course of politics in America. In the 2002 book, The Emerging Democratic Majority, Teixeira and coauthor John Judis asserted their theory that minority voters who prefer Democrats grow as a share of the electorate by 2...