U.S. President Donald Trump has criticized the nuclear deal and said during his election campaign he would stop Iran's missile program.

"Despite four decades of the Islamic system and many promising achievements, people are still suffering chronic problems", he said when announcing his bid last week. Others include a brother of late President Akbar Hashemi Rafsanjani and Tehran's mayor.

According to Article 35 of Iranian election law, people who want to register themselves for the presidential election must have these eligibilities: 1- Religious/ political figure.

"With the deal in jeopardy, the system will be in vital need of Rouhani's team of smiling diplomats and economic technocrats to shift the blame to the USA and keep Iran's economy afloat", said Iran analyst Ali Vaez of the International Crisis Group. But the oil-based economy's struggle to rebound since the lifting of sanctions as part of the nuclear accord could be exploited by Rouhani's hardline foes this time around.

Every Iranian president since Khamenei himself took the presidency in 1981 has won re-election.

Ahmadinejad also voiced reluctant support for Iran's 2015 nuclear deal with the US and other world powers, which saw Iran accept curbs on its nuclear program in exchange for relief from crippling worldwide sanctions.

His main rival in the May 19 elections is expected to be the conservative cleric Ebrahim Raisi, who aligns with the views of the supreme leader, Ali Khamenei, and is the custodian of Iran's holiest shrine.

He said the budget for the armed forces and the Ministry of Defense in the previous Iranian year (which ended on March 20) had increased by about 77 percent compared to three years earlier, adding that the budget for boosting the country's defense capability has risen by 145%. Conservatives say it was political suicide, but analysts say the 61-year-old may simply be trying to put pressure on the Guardian Council to approve his ally Hamid Baghaie. Several former ministers and hardline former president Mahmoud Ahmadinejad are among those who have registered. The supreme leader also serves as the country's commander in chief over its military and the powerful Revolutionary Guard, a paramilitary force involved in the wars in Iraq and Syria that also has vast economic holdings across Iran. He is also a member of Assembly of Experts, an all-cleric body that will rule on the successor for the Supreme Leader.

Iran describes itself as an Islamic Republic. "I think the fact that Raisi is coming, unless he steps aside, it looks very unlikely to me that the nezam [ruling system] would allow Raisi to be humiliated in an election".