The Voting Rights Act was signed into law on Aug. 6, 1965, a year after the murder of three voting rights activists in Philadelphia, Mississippi, and just months after the brutal attack on peaceful protesters in Selma, Alabama. At the signing, President Lyndon Johnson called the act “a triumph for freedom as huge as any victory that has ever been won on any battlefield.” The new legislation was meant to enforce the 15th Amendment, which almost a century before, provided that “The right of U.S. citizens to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude.”

The Voting Rights Act has two main provisions — first, a general prohibition on voting discrimination laid out in Section 2, then a requirement, laid out in Section 5, that states with a history of discrimination receive “preclearance” from the Justice Department before making any changes to voting qualifications, practices or procedures.

The Supreme Court’s decision in Shelby County, Alabama v. Holder struck down Section 4(b), which set out the formula for determining which states are subject to the Section 5 preclearance requirement, thus rendering Section 5 — which many consider the heart of the act — meaningless.

In this week’s Group Think, we ask esteemed lawyers and thinkers what this decision means for the future of our democracy.