Look, as a Christian, I have real problems with Mormonism. Claiming to be part of the Christian faith, Mormonism nonetheless rejects three fundamental tenets of Christian belief:
1. The divinity of Jesus.This is why Christian theologians refer to Mormonism as a "sub-Christian cult."
2. The Trinity.
3. Salvation solely by faith in a gracious God and not our good works.
But frankly, even among Christians who take this view of Mormonism, I detect no prejudice against Mormon officeholders or political candidates and see no reason to suppose that Christians or other Americans would spurn Romney because of his religious affiliation.
There have been numerous prominent Mormons in American national life. Ezra Taft Benson was Dwight Eisenhower's Secretary of Agriculture. Romney's father, who was governor of Michigan following a successful career as an auto executive, was the frontrunner for the 1968 Republican presidential nomination until a comment he made about the Johnson Administration "brainwashing" him on the Vietnam War torpedoed his candidacy. By now, in the American context, these two figures represent ancient history and in the intervening years, Mormonism has become part of the American mainstream.
The only way I can see Romney's Mormonism harming his bid for the 2008 Republican nomination is if he gave indications of an intent to give his faith preferential treatment.
Having said all that, I still think that John McCain is the leading candidate for the Republican nomination in 2008.
UPDATE: Matt at Stones Cry Out thinks that Romney's Mormonism will be a bigger problem than I do.
ANOTHER UPDATE: Hugh Hewitt has also linked to this post. Thanks to both you and Matt!