Iranians will go to the polls today to elect a new President, replacing Mahmoud Ahmadinejad. Six men are on the ballot in the first round; the top two vote-getters will compete in the final round on 21 June.

In an attempt to control the outcome, the regime has sought a consensus candidate from among top politicians most loyal to the Supreme Leader. It has disqualified other candidates, including former President Hashemi Rafsanjani.

That effort at control has been only partially successful and may have backfired.

Who are the candidates?

The regime had hoped to present voters with a single choice from among ‘Principlists’, the dominant faction – including conservatives and hard-liners – in the Islamic Republic in the last decade. However, despite the efforts of a committee backed by the Supreme Leader, there are three leading Principlists on the ballot:

1. Tehran Mayor, Mohammad-Baqer Qalibaf

2. The Supreme Leader's senior advisor and former Foreign Minister,Ali Akbar Velayati

3. The Secretary of the Supreme National Security Council and chief nuclear negotiator, Saeed Jalili

The single choice from among moderates and reformists, who have marginalised following the disputed 2009 Presidential election, is Hassan Rouhani. He is an ally of former President Rafsanjani, a former chief nuclear negotiator, and a senior official with the Expediency Council.

The remaining candidates are Mohsen Rezaei, former head of the Revolutionary Guards, and the independent and lesser-known Mohammad Gharazi.

Who has the best chance of going to the final round?

Among the Principlists, Velayati has a long, high-profile record within the regime, but lacks charisma and his campaign has failed to make much of an impression. Jalili, a last-minute entry, surged in the opening days of the campaign with a sophisticated media effort, but has flagged over the last week with less-than-impressive rallies and a weak performance in the three Presidential debates.

Qalibaf, with eight years as Tehran Mayor and a reputation as a can-do politician, appears to be in a solid position with his concentrated message on management and the economy the leading issue in the campaign.

Rohani started from a weak position, given the regime’s disqualification of his patron Rafsanjani and pressure on the moderates and reformists. However, he has shown more charisma and willingness than other candidates to engage tough issues in speeches and debates, and he has an impressive media campaign that has highlighted Iran's women and youth. He has also benefited this week from the withdrawal of the only reformist candidate, Mohammad Reza Aref, which should unify moderate and reformist voters behind him.

So the outcome is likely to be Qalibaf plus either Jalili or Rouhani – assuming there is no regime manipulation of the vote, as in 2009.

What does this mean for Iran?

The campaign has largely failed to energise Iranian voters so far, especially in comparison to 2009.

If the run-off is between Qalibaf and Jalili, this is unlikely to change. There is not that much distance between the candidates, given their backgrounds and emphasis on loyalty to the Supreme Leader above all else, on economic, political, and culture and social issues. Nor is there likely to be much difference in their approach to foreign policy.

However, if the run-off is between Qalibaf and Rouhani, there may be some enthusiasm and possibility for significant debate. Rouhani has been aggressive in his calls for greater freedoms for Iranians, and he has also emphasised the need to engage with the US and the West on the nuclear issue and other matters. In addition, his involvement will re-open political space cut off for many Iranians – including some in the opposition Green Movement – since the protests of 2009. Symbolically, his presence will draw attention to the plight of political prisoners, specifically the detained opposition leaders and 2009 candidates Mir Hossein Mousavi and Mehdi Karroubi.