Full Disclosure by William Safire (1978): The president is blinded by an assassination attempt while at a summit meeting in the Soviet Union, and an ambitious Secretary of the Treasury attempts to use the 25th Amendment to unseat him.
Give Me Liberty a graphic novel by Frank Miller (1990): An alternate history in which America is led through a time of economic depression and civil uprisings by President Erwin Rexall, who is elected in the year 1996.