Kennedy’s saving grace was that Catholics predominately voted Catholic. With Romney, although Mormons are conservative and are likely to vote Republican, a larger portion of the party is comprised of evangelical Christians and unfortunately Evangelicals and other non-Mormon conservative Christians look with suspicion on the Church of Latter-Day Saints.
The difficulties of a Mormon being elected president are similar to the difficulties of electing a Catholic to that seat. In both cases there is or was the worry that a religious leader would actually be dictating U.S. government policy. Prior to the election of John F. Kennedy, Protestants particularly those that were republicans proclaimed that if Kennedy were President it would be the Pope who was actually running the country. There is a similar feeling among evangelicals that a Mormon President would answer first to the hierarchy of the Church of Latter-Day Saints and to the Constitution second.
Comments and feedback can be sent to firstname.lastname@example.org