It comes as no surprise that black voters prefer Obama or that women prefer Clinton. But why have Hispanic voters chosen Clinton by about the same margin that women have? The two candidates have similar positions on immigration, poverty, English-language teaching... Or do identity politics, in fact, work the other way around? Sergio Bendixen, provoked a furor in late January when he told an interviewer that “the Hispanic voter . . . has not shown a lot of willingness or affinity to support black candidates.” Television commentators treated the claim as accepted wisdom and thus a serious impediment to Obama’s...