Daniel Henninger is deputy editor of The Wall Street Journal's editorial page.

At times even a chief justice of the U.S. Supreme Court finds it useful, as the saying goes, to put the hay down where the goats can get it. And so it was last week in oral arguments over a big voting-rights case.

At issue in Shelby County v. Holder was whether some states in the American South, unlike many states in the North, must still submit any change in voting practices to the Justice Department for approval, as required by one section of the Voting Rights Act of 1965. As Justice Ruth Bader Ginsburg noted, the practical enforcement of this provision is mainly directed at Mississippi, Alabama and Louisiana.

After listening to his liberal colleagues argue that Alabama's election practices, as interpreted by various legal formulas four decades after the law's passage, still discriminate against blacks, Chief Justice John Roberts put the hay down in front of Solicitor General Donald Verrilli....