http://www.mormons.org/basic/doctrines/law/constitution_eom.htm
Latter-day Saints attach special significance to the Constitution of the United States of America. They believe that the Lord "established the Constitution of this land, by the hands of wise men whom [he] raised up unto this very purpose" (D&C 101:80). The Prophet Joseph Smith once described himself as "the greatest advocate of the Constitution of the United States there is on the earth" (Hc 6:56-57). All of his successors as President of the Church have reaffirmed the doctrine of an inspired Constitution.
Latter-day Saints believe that the Lord established the Constitution, not by communicating specific measures through oracles, but by raising up and inspiring wise men to this purpose (see D&C 101:80).
LDS leaders have taught that the Constitution is not to be considered perfect and complete in every detail (as evidenced most clearly by its accommodation with slavery, contrary to modern scripture; e.g., D&C 101:79) but as subject to development and adaptation.