And the best example of all is 1968, when Johnson was discouraged from even being a candidate by anti-Vietnam war pressure, McCarthy’s primary challenge, and RFK in the wings.
I still think Johnson planned to gain the nomination at a brokered convention, which is why he didn’t endorse Humphrey, who did gain the nomination the old-fashioned way.
Of course, by the time of the 1968 Democratic Convention in Chicago, and after the assination of RFK and MLK, and all the “peace” marches and riots, Johnson couldn’t have been nominated for dogcatcher.