Armed agents of “law and order” in Mississippi confront MLK in 1966. Photo: AP Photo During the 30 years since the United States began observing the Martin Luther King Jr. federal holiday, the commemoration of the life and work of this remarkable man has mostly seemed like a backward look at a struggle that largely succeeded. Yes, there have been regular reminders of the unfinished business of the civil-rights movement and the dangers of backsliding on the country’s commitment to equality and