The graphic was splashy by the Census Bureau’s standards and it showed an unmistakable moment in America’s future: the year 2044, when white Americans were projected to fall below half the population and lose their majority status. The presentation of the data disturbed Kenneth Prewitt, a former Census Bureau director, who saw it while looking through a government report. The graphic made demographic change look like a zero-sum game that white Americans were losing, he thought, and could provoke a political backlash. So after the report’s release three years ago, he organized a meeting with Katherine Wallman, at the time...