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).
Twenty-fifth Amendment to the United States Constitution
The Twenty-fifth Amendment (Amendment XXV) to the United States Constitution deals with issues related to presidential succession and disability. It clarifies that the Vice President becomes President (as opposed to Acting President) if the president dies, resigns, or is removed from office; and establishes procedures for filling a vacancy in the office of the vice president and for responding to presidential disabilities. The Twenty-fifth Amendment was submitted to the states on July 6, 1965, by the 89th Congress and was adopted on February 10, 1967.