Fifty years ago, on March 7, 1965, civil rights activists, demonstrating for voting rights, were savagely attacked by Alabama state troopers and vigilantes as they tried to cross the Edmund Pettus Bridge. That day became known as “Bloody Sunday.”

That night, ABC News interrupted the network’s Sunday night movie, “Judgment at Nuremberg,” the Academy Award-winning film about the trials of Nazi war criminals, to show the nation what had happened. The raw footage had no narration and ran for 15 minutes. Viewers, estimated at 48 million, were stunned by the sight of peaceful demonstrators being beaten and tear-gassed. Others who saw news photos of the tragedy had similar reactions — horror, shame and an overwhelming desire to do something. Thousands headed for Selma. Those who could not go south demonstrated in their own communities, from Maine to Hawaii.

Washington was besieged by demonstrators calling for a voting rights act. They obstructed traffic and paraded night and day near the White House, their chanting and singing interrupting the sleep of President Lyndon Johnson and the First Family. Johnson was sympathetic to their demands — in secret, a voting rights bill was being drafted — but he hesitated to announce it because he just had signed the Civil Rights Act of 1964 the previous July, and believed that Congress was not yet ready to pass another major civil rights law.

Bloody Sunday changed everything. Clergymen, congressmen and senators harassed the president, everyone demanding an answer to the same question: “Why has it taken so long for you to send a voting rights bill to the Congress?”

“Two reasons,” Johnson replied. “First, it’s got to pass. We can’t risk defeat or dilution by filibuster on this one. This bill has to go up there clean, simple and powerful. Second, we don’t want this bill declared unconstitutional. This can’t be just a two line bill. The wherefores and the therefores are insurance against that.” ...