The LDS church suffered a schism early on that caused a partial divide between two of the three witnesses from Smith and Sidney Rigdon. Oliver and David, along with the Whitmer family, essentially lead a branch of the church under their leadership in Missouri while Smith and Rigdon lead the Ohio saints for a period. Both groups had problems with their neighbors, but the Ohio saints failed when the Kirkland Anti-bank scheme collapsed. Facing insurmountable creditor claims and opposition, the move of the Smith-branch of saints to recombine with the Whitmer-Cowdery branch resulted in a new crisis of leadership. The failed saints of Ohio, and most importantly Smith and Rigdon, claimed common property with the saints of Missouri. Cowdery and Whitmers were more free-market minded, and felt their success shouldn't be robbed by the Ohio saint's failures.
When Oliver, John and David Whitmer were excommunicated, it was over this challenge of leadership. Oliver began speaking openly about Joseph's affairs as a power move, not because he just found out about it.
You'll notice this dynamic in letters written by Smith and Rigdon from that time, stating they are the presidency of the "whole church of latterday saints". For example, this letter demanding John Whitmer turn over his documented history of the Church:
Mr J. Whitmer
Sir. We were desireous of honouring you by giving publicity to your notes on the history of the Church of Latter day Saints, after such corrections as we thaught would be necessary; knowing your incompetency as a historian, and that your writings coming from your pen, could not be put to the press, without our correcting them, or elce the Church must suffer reproach; Indeed Sir, we never supposed you capable of writing a history; but were willing to let it come out under your name notwithstanding it would realy not be yours but ours. We are still willing to honour you, if you can be made to know your own interest and give up your notes, so that they can be corrected, and made fit for the press. But if not, we have all the materials for another, which we shall commence this week to write.
your humble Servents
Joseph Smith Jr
Sidney Rigdon
Presidents of the whole
Church of Latterday Saints
This is a pattern that is evident throughout the history of Smith as leader.
I strongly contend that the original make-up of the leadership (Smith, Cowdery, David Whitmer) was tied to their all being knowingly involved in the creation of the Book of Mormon. The lost pages written prior to the arrival of Cowdery were a failure, and Smith was debating giving up on their creation when Cowdery arrived. The process that produced the book include both Smith and Cowdery retiring to the Whitmers to be able to work on it, and the Whitmer family was knowledgeable of the scheme. Harris was not part of this leadership group because his only role was to finance the cause. He was a target of the leadership, and his role was never as meaningful once the church was established.
The conversion of Sidney Rigdon, along with his congregation, was a major moment in Church history as well. Had it not happened, it's doubtful we'd all be Mormons. Or in my case, even been born. This was a critical moment that exploded the growth of the Church. But more importantly, Rigdon brought a spark to the theological ideas that made them more appealing and contemporary. It was Rigdon, and his attachment to the Stone-Campbell originalist movements, that gave the restoration meaning and roots in a manufactured original Christianity. And Smith saw his future being in Rigdon rather than Oliver and the Whitmers. Later on, Smith would abandon Rigdon in the Nauvoo Period as John C. Bennett became his new confidant and right hand through the creation and expansion of spiritual wifery. And once Bennett was abandoned, he turned last to his brother Hyrum right before the end.
The three witness were all part of a scheme. The Whitmers went on to start another church using David's claim to being a witness as the source of authority. Cowdery went on to try and leave it behind him, though his sister being married to Brigham Young's older brother, Phineas, meant he was always aware and kept in touch. It was through Phineas that Cowdery explored returning. His letters leading up to it show he was interested in seeing the witness authority reinstated as part of the leadership structure of the Church. Brigham may have entertained it brief during the Succession Crisis following Smith's lynching to bolster his own authority. But once it proved unnecessary for him to take control of the leadership of the main body of saints, Cowdery's approaches were rebuffed. He ultimately did return once his health and financial woes became too much late in his life.