Has any US Presidential nominee/presumptive nominee from a major party, apart from Johnson, withdrawn from the race mid-campaign?

Question

After the recent US Presidential debate between Joe Biden and Donald Trump, the news has been flooded by statements from numerous sources saying essentially this, namely that Biden's performance was so atrocious the Democrats should convince him to withdraw and nominate someone else. Notably, these calls^* are coming from self-identified Democrats and Biden supporters. This piqued my interest since apart from Lyndon Johnson, who as president was the presumptive party nominee, I don't know of a situation where a candidate's performance led to their own supporters calling for a replacement candidate. My attempts at google-fu have run into a wall since most of the searches are now flooded with last night's reactions.

Specifically, I'm interested in situations where: 1- A candidate has been replaced by their own party after winning enough primaries to be the de-facto or actual presidential nominee. 2- Significant elements of a nominee/presumptive nominee's own supporters have called for their replacement mid-campaign. For example, I would not consider Bernie Sander's supporters calling for Barak Obama or Hillary Clinton to reject the nomination, as those supporters always preferred Bernie.

Bonus points if a specific incident turned the candidate's party/supporters from largely pro to against rather than a drawn out series of events.

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^*It's paywalled, but the author says he's a long-time Biden supporter and the debate performance made him "weep." The author calls for Biden to step down and be replaced as the Democratic candidate.

Answer 1

No, I don't believe it has. Certainly not in the modern era of nomination primaries.

Aside from LBJ, the closest I believe was in 1972 when the Democratic vice-presidential nominee was forced to resign over mental health issues, 2 days after the convention. In those benighted days, merely availing oneself of mental health therapy was considered disqualifying. To be fair, the therapy in question is considered very controversial by today's standards as well. He was basically replaced with someone picked entirely by the McGovern campaign.

When the general election came around, its tough to see that replacing the man helped any at all. McGovern won one state, and the District of Columbia.

There was also an eventuality in 2000, when a dead man was elected to one of the two senate seats in Missouri. He also happened to be the Governor, who is the person who would get to appoint someone to fill a vacant Senate seat until the next election. His lieutenant governor promised prior to the election to appoint the wife of the deceased to the position if the deceased were to be elected, and it appears the electorate preferred that option to the man's living opponent.

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While we're on the subject though, I'd like to also bring up Johnson. A man in his position, as the incumbent, would indeed usually be considered the presumptive nominee. However, the Vietnam war was deeply unpopular with his party's electorate, and he was largely tied to it. The current scion of the family of his longtime political rivals, Robert Kennedy had just entered the primary race. LBJ nearly lost the New Hampshire primary to Kennedy (failing to get 50% of the vote), and LBJ's own internal polling was showing that he was going to lose the next primary state to Kennedy, badly.

So no, at that point I don't think it would really be fair to think of Johnson as the "presumptive nominee". In fact his own political research and instincts were telling him otherwise. It seems quite likely he knew his business, at least if Kennedy hadn't been assassinated months later.