(AP Photo/Eric Gay) Elizabeth Santorum, left, listens to her father, Republican presidential candidate and former Pennsylvania senator Rick Santorum, right, during a campaign rally on Sunday in Traverse City, Michigan. I n February 1849, Brigham Young, the man who unified the Church of Jesus Christ of Latter Day Saints, declared that the black man’s color is the mark of Cain—the manifestation of the first capital crime, Cain’s murder of his brother. These days Mormon revisionism doesn’t so much contest as ignore Young’s decree, implying that it’s urban legend. What the Church can’t dispute is that until three decades ago, African Americans were prohibited from playing any role in the Church, and the extent to which they’ve done so since is minimal. Governor Mitt Romney, a lifelong practicing Mormon, never has been keen to discuss this, and one of the ironies of the last few weeks is that he might not have to, if his candidacy continues to deteriorate courtesy of former senator and...