THIS fall, we behold omens that will darken a year hence in the final phase of President Obama’s campaign for a second term. His likely opponent, the Mormon Mitt Romney, will be a pioneer figure whatever the outcome, since no previous member of that very American church, the Church of Jesus Christ of Latter-day Saints, has ever secured a major-party nomination. Even should Mr. Obama triumph, a crucial precedent will have been established.

Mr. Romney, earnest and staid, who is deep within the labyrinthine Mormon hierarchy, is directly descended from an early follower of the founding prophet Joseph Smith, whose highly original revelation was as much a departure from historical Christianity as Islam was and is. But then, so in fact are most manifestations of what is now called religion in the United States, including the Southern Baptist Convention, the Assemblies of God Pentecostalists and even our mainline Protestant denominations...