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 presidential election
The final way to be elected for president is to have one's name written in at the time of election as a write-in candidate. This is used for candidates who did not fulfill the legal requirements to be pre-listed on the voting ticket. It is also used by voters to express a distaste for the listed candidates, by writing in an alternative candidate for president such as Mickey Mouse or comedian Stephen Colbert (whose application was voted down by the South Carolina Democratic Party). In any event, a write-in candidate has never won an election for President of the United States.