What kind of powers does the president actually have?

The exact dimensions of presidential power in Iran are complicated, as shown by this graphic from the 2009 election. The presidency has evolved, starting out weak in the early years of the revolution but taking on greater importance after the abolition of the office of prime minister in the late 1980s. Once in office, presidents now create their own power bases, often clashing with the very people who backed their rise to power. All political struggles in Iran are typically waged under the watchful eye of the country’s supreme leader, Ayatollah Ali Khamenei, who ultimately decides the winners and losers, carefully balancing competing interests, to make sure no faction amasses too much power.

How easy is it to predict who will win?

Iran’s presidential elections, lacking independent opinion polls and subject to manipulation, are notoriously unpredictable. In 2005, Mr. Ahmadinejad came out of nowhere to win. In 2009, millions of people took to the streets to protest what they said was widespread fraud in the voting that returned Mr. Ahmadinejad to office over the opposition candidate, Mir Hussein Moussavi.