In short, never. At least not in the era of modern primaries where people have a chance to vote on who will be the candidate, rather than just party leaders selecting the candidate, which began in the 1970s.
If you go back further in time, there’s been a few incidents where party leaders denied their endorsement to an election incumbent for various reasons.
When was the last time a incumbent president has been defeated by a primary challenger?
In short, never. At least not in the era of modern primaries where people have a chance to vote on who will be the candidate, rather than just party leaders selecting the candidate, which began in the 1970s.
If you go back further in time, there’s been a few incidents where party leaders denied their endorsement to an election incumbent for various reasons.
https://time.com/5682760/incumbent-presidents-primary-challenges/