On June 25, 2013, the U.S. Supreme Court handed down its decision in Shelby County v. Holder, invalidating a key provision of voting rights law. The decision--the culmination of an eight-year battle over the power of Congress to regulate state conduct of elections--marked the closing of a chapter in American politics. That chapter had opened a century earlier in the case of Guinn v. United States, which ushered in national efforts...