Twenty-second Amendment to the United States Constitution
As worded, the primary focus of the 22nd Amendment is on limiting individuals twice elected to the presidency from being elected again. Due to this, several issues could be raised regarding the amendment's meaning and application, especially in relation to the 12th Amendment, ratified in 1804, which states, "But no person constitutionally ineligible to the office of President shall be eligible to that of Vice-President of the United States". While it is clear that under the 12th Amendment the original constitutional qualifications of age, citizenship, and residency apply to both the president and vice president, it is unclear whether someone who is ineligible to be elected president could be elected vice president. Because of this apparent ambiguity, there may be a loophole in the 22nd Amendment whereby a two-term former-president could be elected vice president and then succeed to the presidency as a result of the incumbent's death, resignation, or removal from office (or even succeed to the presidency from some other stated office in the presidential line of succession).
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.