WITH MITT Romney’s candidacy for president, the Mormon church approaches an epochal moment in its deep engagement with American politics. The nation, too, is at a threshold - entering, perhaps, a more spacious public understanding of many once-marginal groups.

In the Mormon case, it’s been a long time coming. Romney may be a front-runner for the Republican nomination, and his father George may once have been a serious candidate for president, but the first Mormon to run for president was the first Mormon himself.

In 1844, as the head of a burgeoning new religious movement that identified the US Constitution as a sacred text inspired by God, Joseph Smith saw politics as a mode of missionizing. He was the mayor of the Mormon enclave in Nauvoo, Ill., where he proposed, to cite one position, that the freedom of slaves be bought with sums raised by the auctioning of public lands. But Smith’s real concern had to be the protection of his own movement from harassment by mobs, which were abetted by local and federal authorities. He ran for president as an independent, and his candidacy was marginal. No matter what, he would have had little impact on an election that gave the nation James K. Polk. But in June, while under arrest, charged with treason, he was murdered in jail.

The early story of the Church of Jesus Christ of Latter-day Saints is a saga of confrontation and dispersal. When the church finally settled in Utah, it went from being a despised minority to a regional power. When challenged by the federal government over polygamy, and when polygamy was then abandoned, the Church of Jesus Christ of Latter-day Saints, or LDS, came into its own as the permanent political pillar of Utah, with ever-increasing influence in neighboring states.

The figure who symbolized the Mormons’ move into the national mainstream was Ezra Taft Benson, who was Dwight Eisenhower’s secretary of agriculture and whose great-grandfather was a close associate of Brigham Young. While in Eisenhower’s cabinet, Benson also served as a member of the church’s governing Quorum of Twelve Apostles, and he would go on to be the church’s president from 1985 until his death in 1994. Mormonism may have begun as a dissident counterculture, but Benson was an icon of the American conservative consensus. In 1966, for example, he authored a pamphlet entitled, “Civil Rights: Tool of Communist Deception,’’ reflecting the right wing’s dual obsessions with communist infiltration and racial integration.