THE CANDIDATES

Hassan Rowhani

Combatant Clergy Association

• Secretary of the Supreme National Security Council for 16 years

• Leading moderate

Saeed Jalili

Islamic Revolution Stability

• Secretary of the National Security Council

• Iran’s chief nuclear negotiator

• Youngest of the candidates

Mohammad Gharazi

Independent

• At 72, he is the oldest candidate

• Strongly criticized the West and the U.S. in their approach toward Iran and its nuclear issues

Mohsen Rezaie

Moderation and Development Party

• Former commander of the Revolutionary Guards

• Ran in 2005 and 2009

Ali Akbar Velayati

Islamic Coalition Party

• Minister of Foreign Affairs from 1981-97

• Focused on Iran’s economic problems and sanctions

Baqer Qalibaf

Islamic Society of Engineers

• Elected mayor of Tehran twice

• Came in fourth in the 2005 presidential race

In the end, Iran’s presidential election may be defined by who doesn’t vote.

Arguments over whether to boycott today’s vote still boiled over at coffee shops, kitchen tables and on social media among many liberal-leaning Iranians on the eve of the voting. The choice — once easy for many who turned their back in anger after years of crackdowns — has been suddenly complicated by an unexpected chance to perhaps wage a bit of payback against Iran’s rulers.

The rising fortunes of the lone relative moderate left in the race, former nuclear negotiator Hasan Rowhani, has brought something of a zig-or-zag dilemma for many Iranians who faced down security forces four years ago: Stay away from the polls in a silent protest or jump back into the mix in a system they claim has been disgraced by vote rigging.

Which way the scales tip could set the direction of the election and the fate for Rowhani, a cleric who is many degrees of mildness removed from being an opposition leader. But he is still the only fallback option for moderates in an election that once seemed preordained for a pro-establishment loyalist.

“There is a lot of interesting psychology going on. What is right? Which way to go?” said Salman Shaikh, director of The Brookings Doha Center in Qatar. “This is what it means to be a reformist in Iran these days.”

Iran’s presidency is a big prize, but not a crown jewel. The president does not set major policies or have the powers to make important social or political openings. That rests with the ruling theocracy and its protectors, led by the immensely powerful Revolutionary Guard.

But for liberal-leaning Iranians, upsetting the leadership’s apparent plans by electing Rowhani could open more room for reformist voices and mark a rare bit of table-turning after years of punishing reprisals for the 2009 protests, the worst domestic unrest in Iran since the 1979 Islamic Revolution.

“Rowhani raises a lot of interesting questions,” said Scott Lucas, an Iranian affairs expert at Britain’s Birmingham University. “Among them, of course, is whether he gets Iranians who have rejected the system to then validate the system by voting again.”

And there are many other factors at play.

Many Iranians say they are putting ideology aside and want someone who can stabilize the sanctions-battered economy — one of the roles that does fall within the presidential portfolio. This could boost candidates such as Tehran Mayor Mohammad Bagher Qalibaf, who is seen as a fiscal steady hand.

Also, the rest of the candidates approved to run by election overseers — from more than 680 hopefuls — are stacked heavily with pro-establishment figures such as hard-liner Saeed Jalili, the current nuclear negotiator. Among those blocked from the ballot was former President Akbar Hashemi Rafsanjani, who is one of the patriarchs of the Islamic Revolution.

The vetting appeared aimed at bringing in a pliant and predictable president after disruptive internal feuds with current President Mahmoud Ahmadinejad, who cannot run for a third consecutive term. Ahmadinejad, who upended Iran’s political order by trying to challenge the authority of Supreme Leader Ayatollah Ali Khamenei. The desire for calm is also fueled by the critical months ahead, which could see the resumption of nuclear talks with the U.S. and other world powers.

But the presumed plans have met an obstacle in the form of Rowhani, who is a close ally of Rafsanjani and is now backed by other reformist leaders who had previously seemed resigned to defeat. In the span of 24 hours earlier this week, Rowhani received a major bump when a moderate rival withdrew to consolidate the support. Endorsements from artists, activists and others poured in.

Rowhani is believed to favor a less confrontational approach with the West and would give a forum for now-sidelined officials such as Rafsanjani and former President Mohammad Khatami, whose reformist terms from 1997-2005 opened unprecedented social and political freedoms.