The President of the Mormon Church is also their prophet during the time he is President. So if said prophet gives a prophecy, and it fails, then he is a false prophet.
Now, some Mormon may say this utterance wasn’t a prophecy, but even if it isn’t, it is an unqualified statement about the future actions of the Mormon Church:
We will not end the practice of plural marriage until the coming of the Son of Man.
President Wilford Woodruff, as quoted by Journal of John Henry Smith, 21 May 1888, LDS Church Archives. (H/T Life After Ministry.)
This very same Wilford Woodruff then issued the Manifesto ending polygamy on 25 September 1890, and did so for one reason — so that Utah could be admitted to the Union. (And also to regain assets escheated to the U.S. Government, of course.)
Now Mormons consider this manifesto to have been prompted by divine revelation, i.e., Woodruff was acting in accordance with a revelation from God, even though the Manifesto itself wasn’t a direct revelation. I know, it’s confusing, so let’s clarify this. According to Wikipedia, “Woodruff later said that on the night of September 23, 1890, he received a revelation from Jesus Christ that the church should cease the practice of plural marriage.” So apparently a direct revelation was given to Woodruff to cease polygamy, but the Manifesto wasn’t the revelation itself.
However, some plural marriages were still being performed to the point where another “Manifesto” was issued by LDS President Joseph F. Smith in 1904 stating that the LDS Church no longer sanctioned polygamous marriages and would excommunicate those who entered such unions.
And yet to add to the confusion, Doctrine & Covenants 132 was a direct revelation to Joseph Smith initiating polygamy (although Smith had been practicing it for years) as an “everlasting covenant; and if ye abide not that covenant, then are ye damned; for no one can reject this covenant and be permitted to enter my glory. …”
So if this was to be an “everlasting” practice, God must have lied to Joseph Smith from the beginning, knowing He would have to stop the practice in 1890. Or did He lie to Wilford Woodruff when he told Woodruff to cease the practice? Or did Joseph F. Smith violate God’s D&C 132 covenant in 1904?
I’ve pointed out before what God’s real view of polygamy is. But Mormons have turned God into a liar by their false prophecies. Either that or they are all damned for not obeying God’s commands in D&C 132!