美國總統歐巴馬（Obama）已進入任期的最後一年。他最近開玩笑說，他的一些支持者希望他能繼續留任。2015年11月，他在紐約對民眾發表講話時說：「他們會說，巴拉克，希望你能再參加一次競選。」
他說：「但我解釋說：第一，這是違反憲法的。喬治·華盛頓(George Washington)樹立了一個好榜樣；第二，即使符合憲法，米歇爾（Michelle）也不會允許；第三，這從來都不是關乎我個人的事。」
所有的美國總統，除一人外，都效仿華盛頓在第二個四年任期到期後離開總統職位。1951年批准的美國憲法第22修正案(The 22nd Amendment to the Constitution)禁止任何人當選總統超過兩次。
1912年的一幅政治漫畫描繪了喬治·華盛頓的幽靈勸阻前總統西奧多·羅斯福(Theodore Roosevelt)尋求第三個總統任期。(National Archives)
有些人不贊同任期限制。他們認為，選民應該能夠保留自己喜歡的總統，同時任期限制也削弱了總統在第二個任期的能力，成為所謂的「跛腳鴨」。
但任期限制有助於推出具有新思維的新候選人，也可防止人們認為某一位領導人是不可或缺的想法。支持者認為，總統職位是一份工作，而不是一個職業。
科羅拉多學院（Colorado College）以總統任期為研究課題的教授託馬斯·克羅寧(Thomas Cronin) 說，「第22修正案算不上很完美，但也是一個很實際的妥協方案，一來考慮到擔任總統一職需要有精力、決斷能力和領導才幹，二來也顧及了輪換執政的共和原則。」
三分之二的美國人支持第22修正案對總統任期的限制。克羅寧說：「大多數美國人都了解，任期限制是為了保護自由不得不在權衡之下做出的取捨。」
Now in his last year in office, President Obama recently joked that some of his supporters would like him to stay on. 「They』ll say, oh, Barack, I wish you could run another term,」 hetold a New York audience in November.
「But I explain: A, it’s unconstitutional. George Washington set a good example. B, Michelle would not permit it, even if it were constitutional. And, C, this has never been about me,」 he said.
All but one of the U.S. presidents followed Washington’s example and walked away from power after their second four-year terms. The 22nd Amendment to the Constitution, ratified in 1951, now prohibits anyone from being elected president more than twice.
A 1912 political cartoon shows former President Theodore Roosevelt being discouraged by George Washington’s ghost from seeking a third presidential term. (National Archives)
Some disagree with term limits. They argue that voters should be able to retain a president they like. Term limits also weaken second-term 「lame duck」 presidents, they contend.
But term limits encourage new candidates with fresh ideas and guard against the notion that any single leader is indispensable. The presidency is a job, not a career, proponents argue.
Thomas Cronin, a professor at Colorado College and expert on the presidency, says, 「The 22nd Amendment [imposing presidential term limits] is a practical if imperfect compromise between the need for energy, decisiveness and leadership in the presidency and the republican principle of rotation in office.」
Two-thirds of Americans support the 22nd Amendment and presidential term limits. 「Most Americans understand that term limits are a trade-off for the protection of liberty,」 Cronin said.