The future of affirmative action in higher education could turn on the definition of “critical mass” — a diversity goal the U.S. Supreme Court established the last time it decided whether universities could consider race when admitting students.

As the justices took up Fisher v. University of Texas at Austin,a challenge to the University of Texas’ affirmative action policy, on October 10, the Court’s moderate-liberal members aggressively challenged Abigail Fisher’s counsel, Bert Rein of Wiley Rein, while the conservative justices aimed their firepower at the university’s advocate, Gregory Garre of Latham & Watkins.