President Obama and Vice President Biden accept the Democratic Party's 2012 presidential nomination for a second term. (© AP Images)

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,” he told 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.

Graphic reading "Elections 2016" (State Dept./J. Maruszewski)