Almost 40 years ago, a 21-year-old Mitt Romney watched as his father's presidential campaign stumbled to a halt. George Romney's 1968 bid for the White House failed for several reasons -- his notorious remark that U.S. generals had brainwashed him into supporting the Vietnam War, the surprise entry into the race of fellow liberal Republican Nelson Rockefeller, Richard M. Nixon's establishment appeal. But his Mormonism wasn't among them.

"I don't recall ever having been asked about his beliefs or about the Mormon church," says Charles Harmon, the elder Romney's press secretary at the time. Walter DeVries, Romney's chief strategist during the race, never considered his boss's religion a political liability. "I just don't remember it coming up," he notes.

George Romney's candidacy did spark some news stories about the refusal of the Church of Jesus Christ of Latter-day Saints to allow blacks to join the priesthood, a policy that was reversed in 1978. But his strong civil rights record as governor of Michigan inoculated him against charges of racism, and reporters otherwise paid virtually no attention to his religion.

So how, four decades later, has Mormonism become a major factor, and perhaps the defining challenge, in Mitt Romney's race for the White House? Is it possible that the country has grown less tolerant? When it comes to putting a Mormon in the White House, the answer may be yes. In February, a Gallup poll showed that more than a third of Americans would not vote for a Mormon or had reservations about doing so.

"George Romney ran in the shadow of the Kennedy election in 1960, when the country decided religion didn't matter," says Richard Lyman Bushman, a Mormon scholar and professor emeritus of history at Columbia University. "Now it seems like we are working through all the issues that troubled Kennedy, but in a Mormon mode."...