Has an incumbent president ever lost a primary?

Related questions

1. Can an incumbent president be challenged in a primary?
2. How many incumbent presidents have lost?
3. How does the caucus process work?
4. How many presidents have been impeached?
5. Is Vice President Biden running for president?
6. Is Bernie running in 2020?
7. When did Joe Biden run for president?
8. What is the 2020 primary schedule?
9. What is the point of a caucus?
10. How long is Donald Trump's presidency?

Tags

1. #election
2. #there
3. #president
4. #carter
5. #losing
6. #close
7. #reagan
8. #primary
9. #speaking
10. #bruising
11. #kennedy
12. #incumbent
13. #running
14. #challenger
15. #answer
16. #fight
17. #although
18. #never
19. #strictly