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).
Term limits in the United States
In 1940, Franklin D. Roosevelt (president, 1933–1945) became the only president to break the tradition, winning a third term in 1940 and a fourth term in 1944. This gave rise to a successful move to formalize the traditional two-term limit by amending the U.S. Constitution. As ratified in 1951, the Twenty-Second Amendment provides that "no person shall be elected to the office of President more than twice". The new Amendment explicitly did not apply to the incumbent, President Harry S. Truman. However, Truman's close advisors convinced him not to seek a third term regardless, pointing to his age, his failing abilities, and his poor showing in the polls.