Then there's polygamy, introduced by Joseph Smith (who had 49 wives) and practiced until, a century ago, the church finally realized that the federal government would not tolerate it. And there's church and state: Some people fear that, deep down, Mormons want to gain control of the government and turn the United States into their kingdom of God.

Some of those objections might fade if voters got to know a Mormon of compelling political credentials and came to feel comfortable with him. Other objections might have to be answered directly. In regard to polygamy, for example, it would be unfair to hang that history around the neck of Romney, the husband of one and only one wife since their marriage 36 years ago.

As for church and state, Mormons don't seem especially threatening to the prevailing order. The church doesn't endorse candidates. It stays out of partisan matters, refusing even to let individual churches or their membership lists be used for partisan purposes. It does encourage citizens to vote: Before elections the church urges members to consider the issues and candidates, "and then vote for the people that best represent their ideas of good government," according to a spokesman.

Like most churches, it participates in law cases raising religious-liberty issues, often partnering with religious bodies of diverse beliefs. Here, in a friend-of-the court capacity, the church seeks to protect its ability to proselytize and to hire church officials and employees. The church rarely joins an Establishment Clause case. It stays out of public aid cases as a matter of church doctrine, since it doesn't accept government funds to assist with any of its operations. It didn't participate in last year's Pledge of Allegiance case in which "under God" was at issue or in the Ten Commandments cases heard by the Supreme Court in the current term.

The church does occasionally speak out on what it calls "matters of principle." In the 1970s and early 1980s, it helped defeat the Equal Rights Amendment. More recently it has affirmed the traditional definition of marriage and contributed to referendum drives banning same-sex unions. The church seems to distinguish ballot-measures from elections for office, seeing only the latter as partisan. In any case, the church's efforts in these respects have a common theme — protection of the traditional family. It is a defensive posture.

Again, if Romney runs, voters will be confronted not with Mormonism in general but with a particular Mormon. Romney grew up in the church and, as is typical, was baptized at age 8, joined the priesthood at 12, and became an elder when he was 18. In his early 20s, he served as a missionary in France. "Most of each day," he recalls, "was spent responding to: 'You are American, aren't you? Well, get out of Vietnam!' " Romney has served as a Sunday school teacher. He also tithes, as Mormons are expected to, and gives generously to those with special needs.