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).
Dual mandate
Unlike many federations, U.S. states do not generally restrict state or federal officials from seeking office at another level of government without resigning their existing offices first. For example, in the four U.S. presidential elections contested from 1988 to 2000 inclusive, three sitting state governors were nominated for the presidency, these being Michael Dukakis in 1988, Bill Clinton in 1992 and George W. Bush in 2000 (Clinton and Bush were elected president), while in 2016 sitting governor Mike Pence was elected vice president. Elsewhere, serving state officials often seek federal office, one prominent example being Illinois State Senator Barack Obama's election to the United States Senate in 2004 - Obama quickly resigned from the Illinois Senate after being elected to the U.S. Senate despite not being legally required to do so, and served as a U.S. senator until 2008 when he was elected president. Also, it is not uncommon for sitting federal officials to contest election to state offices, although in these cases the office sought is usually one of the state's highest political posts, typically governor - one such recent example being the aforementioned Mike Pence who was a sitting U.S. Representative when he was first elected governor.