Here is a funny thing to contemplate: if Barack Obama were running in the current election, he'd probably win a third term. His most recent job approval rating of 54 percent is one of the highest for a president before the election since modern polling began. It also suggests that he is far more popular than the two major candidates to succeed him, both of whom have strong negatives. The only problem, of course, is a bit of the constitutional text that prohibits him from running, namely the 22nd amendment, which limits the president to two terms.
Term limits are of ancient origin and date back to the ancient Greeks. The American founding fathers thought about adopting term limits for the presidency in our foundational text, but declined to include them. Constitutional silence on the matter, however, did not prevent an informal norm from emerging. George Washington left office after two terms and set a precedent that would be followed by the next thirty presidents, including some, such as Thomas Jefferson and Andrew Jackson, who could easily have won a third term. As early as 1839, John Quincy Adams was calling the two-term limit a "tacit subsidiary constitutional law." Later in the nineteenth century, when President Ulysses S. Grant was considering running for a third term, a popular outcry declared the rule to be an unwritten constitutional norm.
The scope and limits of this unwritten norm, however, became an issue when Theodore Roosevelt sought to run on his independent Bull Moose ticket in 1912. Roosevelt had succeeded to the presidency in 1901 after the assassination of William McKinley in 1901, and had served through 1908 after winning his own election. He then decided not to run again, but four years later changed his mind. During the 1912 campaign, Roosevelt was shot by a madman who justified his actions on the grounds that two terms was the maximum allowed. (Roosevelt finished his speech before seeking medical care, but didn't win the presidency.) The 1912 winner, Woodrow Wilson, made noises about a third term in 1920, but was too unpopular to have a chance at it.
When another Roosevelt, Theodore's cousin Franklin Delano, ran for a third term in 1940, it was considered to be a major break with tradition, but also one that was subsequently blessed with his large margin of victory over Wendell Willkie. In 1947, however, two years after Roosevelt's death, the Republican Party introduced the 22nd amendment to formalize the informal rule, and it was ratified in 1951. Since then, only constitutional law scholars spend much time thinking about third terms, conjuring scenarios in which, say, Bill Clinton is named Vice-President and then succeeds his impeached spouse (all hypothetical of course).
Outside the United States, term limits are popular. As colleagues and I discovered, some 60% of constitutions that have a fixed term head of state place some limit on the number of terms that can be served. Term limits have been very popular in Latin America, and are often effective when leaders want to overstay their terms: Colombia's Alvaro Uribe, for example, was prevented by the Constitutional Court from holding a referendum on amending the constitution to seek a third term in 2010. In 2009, President Manuel Zelaya of Honduras was removed from office after threatening to seek a second term. But in other countries, courts have been more compliant. Nicaraguan strongman Daniel Ortega was allowed to run for a third term (which he won yesterday) after courts ruled that term limits were undemocratic as they restrict the will of the majority.
There is something to this point. In a democracy, the people are supposed to choose the leader. Why should we leave the most popular, experienced person out of the running? While there is a risk of someone staying too long, there may be ways to deal with this. Our proposal was to have a superescalating majority requirement. Here's how it would work. If the first election requires a mere plurality of votes, the second would require an absolute majority of votes, so that one would have to get 50% of all votes cast. Each subsequent election would require 5% more of a majority, so that eventually every president would exhaust their support. Under our scheme, Obama would have to get 55% of the vote for a third term; apparently this year's election would still be razor-close, but we'd have an alternative that was truly popular with the American people.