Watergate is so engrained in modern American culture that the suffix -gate essentially means scandal. When the Watergate story broke was there a different definitive scandal, or set of scandals, it was compared to. Or was Watergate unique in its entrenchment into American culture?
The previous presidential-level scandal that continued to echo through the decades was Teapot Dome - and one continues to hear references to it. In the early 1970s, Teapot Dome was fifty years old, while Watergate is now a little over forty years old, to lend some perspective. Perhaps someone would have primary source evidence for the comparison of Watergate to Teapot Dome as Nixon's troubles unfolded, since I believe that is the obvious place to go. I recall that comparison being made as Watergate emerged as a problem, 1972 to 1974, but that is a personal recollection that needs to be verified by written documentation.