Ayatollah Khamenei and the rest of the establishment could simply choose to disqualify Mr. Ahmadinejad, as a vetting council they control is expected to do to hundreds of others who have registered as candidates. But responding to Mr. Ahmadinejad’s desire for a political rebirth might require a more finessed response, analysts said.
President Hassan Rouhani is favored to win re-election. But many Iranians have been disappointed over the lack of economic recovery after the nuclear deal Iran reached with the United States and other major powers. Iran’s hard-liners strongly dislike Mr. Rouhani’s desire to reach out to the West and even to the United States. They accuse him of wanting to smooth the sharp edges of Iran’s ideology and being too willing to consider compromises on cultural issues.
The hard-liners have seized on popular discontent over the economy, and they tried to undermine and pressure Mr. Rouhani where they could. About a dozen pro-Rouhani activists who oversaw social media pages have been arrested in recent weeks. Mr. Rouhani’s brother, Hossein Fereydoun, was summoned to court last week on allegations of corruption. Morality police officers, whom Mr. Rouhani had promised to remove from the streets during the 2013 presidential campaign, are back and arresting women deemed to be wearing their Islamic scarves improperly.
Mr. Ahmadinejad, meanwhile, has been quietly trying to rebrand himself. Ever since his fallout with Ayatollah Khamenei in 2013, which was over the selection of the minister of intelligence, a position that requires the supreme leader’s approval, Mr. Ahmadinejad has been presenting himself as an anti-establishment figure — someone who is not afraid to ignore the will of Ayatollah Khamenei.
At a news conference last week, Mr. Ahmadinejad was reminded of a remark last year by Ayatollah Khamenei in which he hinted that he had told Mr. Ahmadinejad not to run again for office. “This was only an advice, not an order,” Mr. Ahmadinejad told reporters.
Supporters of Mr. Rouhani carefully welcomed Mr. Ahmadinejad’s decision to register as a presidential candidate. “Ahmadinejad registering is a big plus for Rouhani,” said Hossein Ghayoumi, a cleric who supports Mr. Rouhani. “He is planning to fight with the hard-liners, not us. Let them be.”
In their election calculations, hard-liners have been lining up behind Ibrahim Raeesi, a former judicial official. Many of them hope that Mr. Raeesi will one day succeed Ayatollah Khamenei as the supreme leader, and they think having executive experience would increase his chances. Mr. Raeesi currently heads the extremely powerful Imam Reza Foundation in Mashhad, in the east of Iran. But his credentials are tainted by accusations that he was involved in a so-called death committee that issued verdicts that led to the executions of thousands of political prisoners in 1988.
Many Iranian news outlets had been predicting that the presidential race would fundamentally pit Mr. Rouhani, the incumbent, against Mr. Raeesi, the challenger favored by hard-liners. But Mr. Ahmadinejad, at his news conference last week, suggested a three-way contest.
Hamidreza Taraghi, a hard-line political analyst who supports Mr. Raeesi, noted that an aide to Mr. Ahmadinejad, Hamid Baghaee, had also registered as a candidate on Wednesday. “In his dreams he might envision a sort of Putin-Medvedev interplay, where he or one of his aides can hold power,” Mr. Taraghi said of Mr. Ahmadinejad.
The Guardian Council, a 12-member committee that vets the candidates, will announce on April 26 which candidates it determines are qualified to run. Usually, hundreds of hopefuls are disqualified because the council decides they are insufficiently Islamic or because their plans are not in line with the Islamic republic’s ideology.
Most analysts think Mr. Ahmadinejad is not likely to make the cut, unless he can make a significant show of support. He would have to mobilize his supporters over the next two weeks, said Hojjat Kalashi, a sociologist who is critical of the establishment.
“If he can’t show that he still has supporters, they will easily disqualify him,” Mr. Kalashi said.
Mr. Ahmadinejad has called upon his supporters to gather on Friday in East Tehran, a middle-class area where he has lived most of his life. But the authorities seldom allow large gatherings, and the area around his house can easily be cordoned off by the security forces.
Whatever the outcome, Mr. Ahmadinejad’s decision to seek another run for the presidency presents a dilemma to Iran’s establishment. “Both a qualification or a disqualification will be costly for the ruling establishment,” Mr. Taraghi, the hard-line analyst, said. “Just how costly remains to be seen.”