My response is always the same: Mormons have more in common with the values of mainstream American Christian denominations than do Jews. Would we be having this same debate over a Jewish candidate? I really don't think so.
Judaism is close to 4,000 years old, and is accepted as the pre-curser of Christianity by all Christians.
Mormonism is not quite 180 years old, and is seen as a very odd cult built on ridiculous fabricated evidence, by an oversexed fraud.
BIG DIFFERENCE!
Personally I would be highly suspect of anyone who really believes the tenents of the LDS--and I wouldn't want a President so gullible.