Any transition comes at the most crucial time in the 35-year history of the Islamic Republic due to unprecedented domestic political shifts underway and, more importantly, due to international events.

Pragmatic conservative President Hassan Rouhani's election in June 2013 elections led to a social, political and economic reform program facing considerable resistance from within the hard-right factions within the clerical and security establishments. The biggest issue between the presidential camp and its opponents is the ongoing process of negotiations with the United States over the Iranian nuclear program.

Nuclear Talks and Syria

After an unprecedented breakthrough in November 2013 that saw an interim agreement, the negotiation process has hit a major snag, with a final agreement not reached by a July 20, 2014, deadline, though the deadline for negotiations was extended to Nov. 24, 2014. Some form of partial agreement had been expected, with talks kicking into high gear ahead of the opening session of the General Assembly of the United Nations in New York on Sept. 18.

A mood of pessimism in Tehran has since been reported, however, with senior Foreign Ministry officials prepping the media for the eventuality that the talks might fail. The risk of failure comes from the fact that Rouhani can only go so far in accepting caps on Iran's ability to pursue a civilian nuclear program before his hawkish opponents will gain the upper hand in Iran's domestic political struggle. Stratfor sources say Rouhani did not want to attend this year's General Assembly, but Foreign Minister Mohammad-Javad Zarif reportedly convinced the president that his visit might help the negotiating process.

As if the negotiation itself was not enough of a problem for Rouhani, the U.S. move to support rebel forces in Syria that would fight both the Islamic State and Iran's ally, the Assad regime, is a major problem for Tehran. U.S. and Iranian interests overlapped with regard to the IS threat in Iraq. But in Syria, the United States must rely on anti-Iranian actors to fight IS and the Obama administration seeks to topple the Assad regime. Accordingly, less than a year after the two sides embarked upon a rapprochement, tensions seem to be returning.

A New Supreme Leader

On top of this stressor, uncertainties surrounding Khamenei's health have shifted Iran's priorities to the search for a new supreme leader. The unusual manner in which Tehran continues to telegraph Khamenei's hospitalization to show that all is well — while at the same time psychologically preparing the country and the outside world for the inevitable change — coupled with the (albeit unverified) 2010 release by WikiLeaks of a U.S. diplomatic cable reporting that the supreme leader was suffering from terminal cancer suggests the political establishment in Tehran is preparing for a succession. Khamenei himself would want to prepare a succession before he can no longer carry out his official responsibilities.

Before Khamenei was elected supreme leader in 1989, the idea of a collective clerical body was in vogue among many clerics. The country's second-most influential cleric, Ayatollah Ali Akbar Hashemi Rafsanjani, on several occasions has proposed a "jurisprudential council" consisting of several top clerics as an alternative to the supreme leader's post. His proposal has not gained much traction, but with succession imminent, it might seem more attractive as a compromise should the competing factions prove unable to reach a consensus.

Constitutionally, an interim leadership council takes over should the incumbent supreme leader no longer be able to carry out his duties until the Assembly of Experts elects a successor. Considering the factionalized nature of the Iranian political elite, it is only normal to assume that the process to replace Khamenei will be marred by a major struggle between the various camps that make up the conservative establishment. After all, this is an extremely rare opportunity for those seeking change and for those seeking continuity to shape the future of the republic.

For the hardliners, already deeply unnerved by what they see as an extremely troubling moderate path adopted by Rouhani, it is imperative that the next supreme leader not be sympathetic to the president. From their point of view, Khamenei has given the government far too much leeway. For his part, Rouhani knows that if his opponents get their way in the transition, his troubles promoting his domestic and foreign policy agenda could increase exponentially.

Possible Successors

The country's elite ideological military force, the Islamic Revolutionary Guards Corps, will no doubt play a key role in who gets to be supreme leader. Likewise, the religious establishment in Qom will definitely have a say in the matter. The revolutionary-era clerics who have long dominated the political establishment are a dying breed, and the Assembly of Experts would not want to appoint someone of advanced age, since this would quickly lead to another succession.

Stratfor has learned that potential replacements for Khamenei include former judiciary chief Ayatollah Mahmoud Hashemi Shahroudi, a cleric close to Khamenei and known for his relative moderate stances. They also include Hassan Khomeini, the oldest grandson of the founder of the republic, Ayatollah Ruhollah Khomeini. He is close to the president's pragmatic conservative camp and the reformists, but pedigree may not compensate for his relatively left-wing leanings and his relatively young age of 42. Finally, they include current judiciary chief Mohammed-Sadegh Larijani, the younger brother of Speaker of Parliament Ali Larijani who some believe is the preferred candidate of the Islamic Revolutionary Guards Corps.

The key problem that has surrounded the post of the supreme leader since the death of the founder of the republic is the very small pool of potential candidates to choose a replacement from: Most clerics either lack political skills, while those that do have political savvy lack requisite religious credentials. Khamenei was a lesser cleric to the status of ayatollah shortly before assuming the role of supreme leader, though he has demonstrated great political acumen since then. Khomeini was unique in that he had solid credentials as a noted religious scholar, but also had solid political credentials given his longtime leadership of the movement that culminated in the overthrow of shah in 1979. Since Khomeini fell out with his designated successor, Ayatollah Hossein-Ali Montazeri, in 1987, no one has had both qualities. Whoever takes over from Khamenei will be no exception to this, even though he will need to be able to manage factional rivalries at one of the most critical junctures in the evolution of the Islamic Republic.