Timeline of the White Horse Prophecy
Edwin Rushton dies in Salt Lake City.
In the October 1918 General Conference, Joseph F. Smith condemned the White Horse Prophecy as a "ridiculous story" and not a true prophecy of Joseph Smith.
The Church issues an official statement concerning the White Horse Prophecy stating it is "based on accounts that have not been substantiated by historical research and is not embraced as Church doctrine."
What is the White Horse Prophecy?
It's a prophecy Joseph Smith[BIO] allegedly gave on or about May 7, 1843. The prophecy was an elaborate apocalyptic vision that describes global turmoil and war and used symbolic colored horses (white, pale, red, and black) to represent different elements of the vision.
Did Joseph Smith actually give the White Horse Prophecy?
There are no corroborating historical records referencing the prophecy from pioneer-era or early Utah publications or journals nor any record contemporary with Joseph Smith.
Sources for the White Horse Prophecy
Undated but estimated to be no earlier than 1885 and no later than 1902.
"original source" or "Manuscript 3771"
Undated but estimated to be no earlier than 1868 and no later than 1902.
"revised source" or "Manuscript 7897"
March 2, 1902 
"hearsay source" found in John J. Roberts, Reminiscences and Diaries, 1898-1902.
What are the actual contents of the White Horse Prophecy?
Did the belief that the U.S. Constitution would one day "hang by a thread" originate with the White Horse Prophecy?
No. James Burgess recalled Joseph Smith predicting the Constitution would hang by a "brittle thread." This teaching from Joseph Smith was corroborated by Brigham Young, Orson Hyde, and Eliza R. Snow.
Why is the prophecy so well known despite it probably being fake?
The press has brought the White Horse Prophecy up on several occasions when Latter-day Saints have run for political office.
Does the White Horse Prophecy mean that a Mormon is going to run for president and take over the United States?
No. There's nothing in the prophecy that says anything like that.
Do members of the Church plan on some sort of political revolution? Does the "constitution hanging by a thread" mean that Church members think the government needs to be overthrown?
No. The Church affirms only peaceful political activities, not violent activities such as overthrowing a democratically elected government.
Does the prophecy promote violence?
No, not really. The prophecy is about war and destruction and refers to warring countries (France, England, Russia, and others) but does not call Latter-day Saints to be violent.
The "white horse" (Latter-day Saints) is said to draw people from all nations because "they would not <take up> the sword against their neighbors."
Have any other prophets or apostles referenced the White Horse Prophecy?
Yes, but only to denounce it.
However, Church leaders have referenced the teaching that the U.S. Constitution will "hang by a thread." This teaching is included in the prophecy, but Joseph Smith also taught it several years before.
Has the Church made any official statements related to the prophecy?
Yes, the Church in December 2009 issued a statement rejecting the authenticity of the White Horse Prophecy. Church leaders have also condemned it in General Conference and in other contexts.