When the Supreme Court struck down race-based admissions at Harvard and the University of North Carolina two years ago, it reaffirmed a fundamental legal principle: Every American must be treated as an individual rather than as a representative of a racial group. That principle is as essential in the voting booth as it is in the classroom, and next week, the Supreme Court will hear a case— Louisiana v. Callais —that will give it the opportunity to extend it to the ballot box. The case is a