The office of the president is considered to be revolutionary, in the sense that the powers of office are derived from the Revolutionary Constitution of 1917. Another legacy of the Mexican Revolution is the Constitution's ban on re-election. Mexican presidents are limited to a single six-year term, called a "sexenio". No one who has held the post, even on a caretaker basis, is allowed to run or serve again. The constitution and the office of the President closely follow the presidential system of government.