Fifty years ago, when we marked the Gettysburg centennial, we were still fighting a very significant part of the Civil War. That spring, in the name of public safety, Bull Connor, the commissioner of public safety for Birmingham, Ala., unleashed dogs and had fire hoses turned on peaceful civil rights demonstrators. People gave their supreme efforts, and, in some cases, their lives to establish that such injustice, in the name of security, could never be visited upon Americans because of the color of their skin. But the preservation of the rights of a free people requires constant vigilance. It requires our never-ending engagement.