Along with many other plagerisms, mormonism has claimed the "White Horse Prophecy" for itself. Nothing to do with the Biblical White Horse.
According to the so-called "White Horse Prophecy," the U.S. Constitution will be hanging by a thread and a church elder from Zion will ride in on a metaphorical white horse and save it.
This popular prophecy of Smith's is explained in the Encyclopedia of Mormonism:
LDS attachment to the Constitution has been further encouraged by an important oral tradition deriving from a statement attributed to Joseph Smith, according to which the Constitution would "hang by a thread" and be rescued, if at all, only with the help of the Saints. Church President John Taylor seemed to go further when he prophesied, "When the people shall have torn to shreds the Constitution of the United States the Elders of Israel will be found holding it up to the nations of the earth and proclaiming liberty and equal rights to all men" (JD 21:8). To defend the principles of the Constitution under circumstances where the "iniquity," or moral decay, of the people has torn it to shreds might well require wisdom at least equal to that of the men raised up to found it. In particular, it would require great insight into the relationship between freedom and virtue in a political embodiment of moral agency. (Encyclopedia of Mormonism, Vol.1, 1992)
THIS is why the mormons are mourning now. Their valiant Saint failed to fulfill this important task.