What is the fine-grained topic of the following text: Previous incumbent presidents who did not finish first include Harry Truman in 1946-1947 and 1950-1952, Lyndon Johnson in 1967-1968, Richard Nixon in 1973, Gerald Ford in 1974-1975, Jimmy Carter in 1980, and George W. Bush in 2008. Only return the topic.
Incumbent US Presidents not finishing first in their terms