Last week, more than 100 years late, Alabama took an important step toward excising a toxic slice of white supremacy from its Constitution and restoring voting rights to perhaps thousands of people, disproportionately black, with criminal records.

At the state’s constitutional convention in 1901, lawmakers amended the Constitution to bar from voting anyone convicted of a crime involving “moral turpitude.” They didn’t define the phrase, but they were crystal clear about its intent: to preserve “white supremacy in this state” and fight the “menace of Negro domination” at the ballot box, as the convention’s president said.

Authorities took advantage of the term’s vagueness to apply it to offenses, even misdemeanors, that recently freed blacks were far more likely to be charged with. “The crime of wife-beating alone would disqualify 60 percent of the Negroes,” one lawmaker said at the time.

The Supreme Court struck down the provision as racially discriminatory in 1985, but lawmakers revived it by restricting it to felonies. Its definition remained in the hands of local voting registrars, meaning that people with convictions had no idea whether they were prohibited from voting; their eligibility often depended on what county they lived in. It has continued to fall heavily on blacks — nearly one in five of whom are disenfranchised statewide, more than triple the rate for whites. In all, about a quarter million Alabama residents, or 8 percent of the voting-age population, can’t vote because of a criminal conviction.