In August 1966, Hugh B. Brown told two BYU professors that Benson had "a letter from President McKay endorsing his candidacy." Brown said "it would rip the Church apart" if Benson released the letter to the public as part of the presidential campaign.
Of this, Benson's biographer tells the following. As early as October 1965 Benson had asked the church president for permission to campaign as U.S. presidential candidate. McKay told him not to campaign actively but did not require him to decline the efforts of others to draft him as a presidential candidate. Benson decided to withhold knowledge of any of these discussions from his own quorum which learned of his possible presidential candidacy from the newspaper announcement in May 1966.
[Brown interview by Richard Wirthlin and Ray Hillam, 9 Aug. 1966,3, transcribed 11 Oct. 1966 "from Rough Draft Notes," folder 6, Hillam Papers, and box 34, Buerger Papers; Dew, Ezra Taft Benson, 383-84, 386, 392-93. From D. Michael Quinn, Ezra Taft Benson and Mormon Political Conflicts, Dialogue: A Journal of Mormon Thought 26:2 (Summer 1992), also in Quinn, The Mormon Hierarchy: Extensions of Power Salt Lake City (Signature Books, 1994), Chapter 3.]