Twenty-second Amendment to the United States Constitution
Some argue that the 22nd Amendment and 12th Amendment bar any two-term president from later serving as vice president as well as from succeeding to the presidency from any point in the presidential line of succession. Others contend that the original intent of the 12th Amendment concerns qualification for "service" (age, residence, and citizenship), while the 22nd Amendment, concerns qualifications for "election", and thus (strictly applying the text) a former two-term president is still eligible to "serve" as vice president (neither amendment restricts the number of times an individual can be elected to the vice presidency), and then succeed to the presidency to serve out the balance of the term (though prohibited from running for election to an additional term).
President of the United States
Since the amendment's adoption, five presidents have served two full terms: Dwight D. Eisenhower, Ronald Reagan, Bill Clinton, George W. Bush, and Barack Obama. Both Jimmy Carter and George H. W. Bush sought a second term, but were defeated. Richard Nixon was elected to a second term, but resigned before completing it. Lyndon B. Johnson, having held the presidency for one full term in addition to only 14 months of John F. Kennedy's unexpired term, was eligible for a second full term in 1968, but withdrew from Democratic Primary. Additionally, Gerald Ford, who served out the last two years and five months of Nixon's second term, sought a full term, but was defeated by Jimmy Carter in the 1976 election.