The Supreme Court on Tuesday effectively struck down the heart of the Voting Rights Act of 1965 by a 5-to-4 vote, ruling that Congress had not provided adequate justification for subjecting nine states, mostly in the South, to federal oversight. “In 1965, the states could be divided into two groups: those with a recent history of voting tests and low voter registration and turnout, and those without those characteristics,” Chief Justice John G. Roberts Jr. wrote for the majority. “Congress based its coverage formula on that distinction. Today the nation is no longer divided along those lines, yet the Voting...