George Romney addresses the Constitution "hanging by a thread" in a 1967 interview with Dialogue.
Eugene England, Joseph Jeppson, Paul Salisbury, and George Romney, "A Man's Religion and American Politics: An Interview with Governor Romney," Dialogue: A Journal of Mormon Thought 2, no. 3 (Autumn, 1967): 25
DIALOGUE: The L.D.S. people talk about a time when the Constitution will " hang by a thread " and about the saving role of Mormon leaders in the government during such a time. Would you tell us your interpretation of the Constitution "hanging by a thread " and whether you think that such a condition is present now or will be in the foreseeable future?
ROMNEY: Anyone can look at the words of the Prophet Joseph Smith in this respect, as reported by Brigham Young and others who apparently heard him make the statement. I have always felt that they meant that sometime the question of whether we are going to proceed on the basis of the Constitution would arise and at this point government leaders who were Mormons would be involved in answering that question.