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).
United States Constitution
The Twenty-fifth Amendment (1967) clarifies what happens upon the death, removal, or resignation of the President or Vice President and how the Presidency is temporarily filled if the President becomes disabled and cannot fulfill the responsibilities of the office. It supersedes the ambiguous succession rule established in . A concrete plan of succession has been needed on multiple occasions since 1789. However, for nearly 20% of U.S. history, there has been no vice president in office who can assume the presidency.