Iranian President Hassan Rouhani waves to media as he arrives at the Interior Ministry in Tehran earlier this month to register his candidacy for the May 19 presidential elections. (Vahid Salemi/AP)

Iran’s short, intense presidential campaign kicks off Friday with the first televised debate featuring six candidates in a race widely seen as a referendum on whether Iranians feel they have benefited from the nuclear deal that took effect last year.

The May 19 vote will see the moderate incumbent, President Hassan Rouhani, facing off against conservative and reformist challengers, including a hard-line cleric with backing from the country’s religious establishment.

Iran’s influential Guardian Council, a body of senior clerics and jurists appointed by the supreme leader, vets the candidates each election. This year, Rouhani’s approved challengers include the hard-line mayor of Tehran, Mohammad Bagher Ghalibaf; a conservative former culture minister, Mostafa Mirsalim; Vice President Eshaq Jahangiri, a moderate; and former vice president Mostafa Hashemitaba, a reformist.

Also on the list, which was whittled down from the 1,600 or so who initially registered, is Ebrahim Raisi, a confidant of Iran’s supreme leader, Ayatollah Ali Khamenei, and the man now viewed as Rouhani’s main rival. When the Guardian Council weighed in last week, it disqualified former president and populist firebrand Mahmoud Ahmadinejad.

A supporter hands out pictures of cleric Ebrahim Raisi, a conservative presidential candidate backed by Iran’s religious establishment, at a campaign rally in Tehran on April 26. (Ebrahim Noroozi/AP)

Raisi, a cleric with a bloody past as one of several judges who oversaw mass executions of political prisoners in 1988, has been mentioned as a possible successor to Khamenei. The supreme leader dictates Iran’s military and foreign policy, but whoever wins the presidency could nevertheless ultimately determine the tone of Tehran’s engagement with the world and with a more confrontational Trump administration.

The race was expected to be a cakewalk for Rouhani, who oversaw the negotiations that lifted many sanctions against Iran in exchange for constraints on its nuclear program. Most Iranian presidents have coasted to second terms.

But the moderate leader is facing head winds in the wake of the deal he championed, and many Iranians say their living standards have not improved as they expected.

Rouhani’s opponents have attacked him over the sluggish economy, blasting his strategy of opening up to the West in the hopes of attracting more investment. According to the International Monetary Fund, Iran’s real gross domestic product grew by 7.4 percent over the past year — but the growth was mainly due to oil exports. Unemployment runs over 12 percent.

In an authoritarian country such as Iran, which hinders the work of independent journalists and pollsters, political predictions are notoriously inaccurate. Dark-horse candidates have emerged at the last minute to sweep to victory. And there is always the issue of how much it actually matters who is president.

“The only thing you can say with decent certainty is that the day after the elections, Ayatollah Khamenei will still be the most powerful man in the country,” said Karim Sadjadpour, an Iran analyst for the Carnegie Endowment.

All six candidates on Friday will participate in the first of three debates, focusing on social issues. That exchange will be followed by debates on politics and the economy.

The nuclear deal will probably be raised in all three, and that could hurt Rouhani, 68.

“Rouhani is suffering in part from his own success,” said Cliff Kupchan, chairman of the Eurasia Group. “Expectations skyrocketed after the deal. But if you ask the average citizen the Ronald Reagan question — Is your life better than it was yesterday? — you’re going to get no. That’s his potential vulnerability.”

In a jab at Rouhani’s Achilles’ heel, Raisi has vowed that, if elected, he will fight poverty, corruption and unemployment. One in four Iranians under the age of 25 is jobless.

Raisi, 56, does not come by populism naturally. He is known to older Iranians as one of four judges on the “Death Commission,” a tribunal that oversaw the executions of 30,000 people in 1988, most of them members of the opposition Mujahideen-e Khalq, or MEK. He wears a black turban, signifying in Shiite Islam that he is a descendant of the prophet Muhammad.

He rose quickly through the ranks and was the attorney general until last year. He is considered a protege of Khamenei, who appointed him to head the Astan Quds Razavi, the largest and wealthiest charity foundation in charge of Iran’s holiest shrine, in the city of Mashhad. Raisi routinely visits poor neighborhoods and villages to distribute sugar and flour, giving him a constituency among working-class Iranians.

If he wins the election, it will increase the likelihood that he will succeed Khamenei, who is 77 and is said to have been treated for prostate cancer. If he loses, his viability diminishes.

As a creature of the religious and judicial establishment, Raisi has advantages that could propel him to victory if moderates and reformists stay home to register their disappointment in Rouhani.

“He doesn’t have to be very popular to win,” said Alireza Nader, an Iran analyst with the Rand Corp. “He’s the regime’s preferred candidate, especially the supreme leader and the Islamic Revolutionary Guard Corps.”

In a close election, that could make the difference.

“Unlike Rouhani, who in 2013 had popular support and not the elite support, Raisi has elite support,” said Behnam Ben Taleblu of the Foundation for Defense of Democracies. “It might be willing to cheat to make him president.”

The election of Raisi could heighten the risk of confrontation between Tehran and Washington. On Wednesday, the cleric said on a television talk show that the United States will back off sanctions only if it “fears” Iran.

“Today, Americans are afraid of the word ‘Iran,’ ” he said, adding: “The solution is not backing down. We must force them to retreat.”

The Trump administration has signaled its willingness to reconsider the nuclear deal and impose stricter sanctions to contain Iran if it continues to conduct ballistic missile tests and expand its influence in the region. Rouhani’s reelection could undermine international support for that strategy.

“If you have an Iranian president who retains confidence among key partners in Europe and Asia, that will necessarily make the Trump administration’s agenda of getting tough more difficult,” said Suzanne Maloney, a Middle East analyst at the Brookings Institution. “If you have someone with a notorious background like Raisi, there will be a different kind of engagement across the board.”

Cunningham reported from Istanbul.