Supporters of Iranian President Hassan Rouhani hold his portrait during a campaign rally at Takhti Stadium in the southwestern Iranian city of Ahvaz on May 16. Rouhani will face conservative jurist Ebrahim Raisi in Friday's election. (Behrouz Mehri/AFP/Getty Images)

The front-runners in Iran's presidential election held massive, dueling rallies in cities across the country this week, mobilizing supporters in stadiums and public squares ahead of Friday's vote.

President Hassan Rouhani is seeking a second term after negotiating a nuclear deal with world powers and has called on voters to give him a mandate to continue to pursue talks with the West. His primary challenger is conservative jurist Ebrahim Raisi, a candidate more likely to pursue a hard-line foreign policy.

The two candidates have fundamentally different visions of Iran's place in the world, and while the Supreme Leader has the final say on all matters of the state, Iranian presidents can still set the tone.

As the incumbent, Rouhani has an advantage: Every Iranian president since 1981 has secured a second term. But Raisi has managed to threaten Rouhani's bid by seizing on concerns about the economy to run a populist campaign. The nuclear deal lifted international sanctions on Iran, but most Iranians have yet to feel the benefits, leaving Rouhani vulnerable.

Raisi's “campaign and its populist economic message continues to score with poor and rural economies,” said Cliff Kupchan, chairman of the political risk firm Eurasia Group. “He continues to hit Rouhani's record on the economy.”

But while Raisi has gained some momentum — the result, observers say, of help from Iran's influential Revolutionary Guard — Rouhani remains the favorite. His campaign events have turned into massive rallies for reformist opposition leaders under house arrest, and has called for conservative leaders to allow more social and political freedoms.

Thursday marked the official end to the campaign, and Iranians head to the polls Friday. If no candidate reaches 50 percent, a runoff will be held on May 26.

Raisi's supporters chant during a campaign meeting at the Mosalla mosque in Tehran, May 16. The outcome of the vote will have major implications for everything from civil rights to relations with Washington. (Reuters)

Raisi greets his supporters during a campaign rally at Imam Khomeini Mosque in the capital Tehran on May 16. (Atta Kenare/AFP/Getty Images)

Raisi's supporters in Tehran on May 16. (Reuters)

Rouhani's supporters hold purple placards, the symbol of his movement, during an electoral campaign gathering in the northwestern city of Zanjan on May 16. (Behrouz Mehri/AFP/Getty Images)

A supporter of Rouhani holds his poster in downtown Tehran on May 10. (Ebrahim Noroozi/AP)

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