Today the country went to the polls with incumbent Hassan Rouhani facing a huge threat from hardliner Ebrahim Raisi.
Supporters of Mr Raisi have held fiery rallies where they chanted abuse towards America while waving controversial Hezbollah flags.
Crowds at his rallies were angry, waving militant flags and quickly became more irate following speeches, according to the Financial Times.
A rally was held this week at the country’s biggest mosque where crowds also chanted “Rouhani, bye bye” and “When the week is done, Rouhani is gone”.
This is in start contrast to rallies for Mr Rouhani, which are normally held in sports stadiums and with a more peaceful air.
A Raisi victory would set alarm bells ringing across the Middle East and in Washington, following two years of quiet progress from a more moderate Mr Rouhani government.
But a growing number of disillusioned Iranians have given Mr Raisi a chance at a shock victory which could destroy the progress made since the a key nuclear deal signed between Iran and the West in 2015.
One attendee at the rally last week told the FT: “We have no hope in the future. Iran is like an old tree that has rotted from within.”
Even despite Mr Rouhani’s more moderate leadership relations between Iran and the USA have cooled in recent months.
On March 24 this year American vessels were threatened by several Iranian fast attack ships. The Iranian Revolutionary Guard trained their weapons on the US flotilla, which was made up of five ships and included the huge aircraft carrier USS George HW Bush.
In response, America deployed helicopters from the warship to hover over the small attack ships. Washington said these helicopters were then also threatened.
Rear Admiral Kenneth Whitesell, commander of the Carrier Strike Group 2, said Iran had been unnecessarily aggressive during the incident, while Iran said the US ships had breached its territory – a claim America denies.
Rear Admiral Whitesell said: “What I don’t like about that is they were in the middle of international transit waters. We had a right to be there as we were exercising freedom of navigation on our way into the Arabian Gulf.
“They also had weapons uncovered as some of the cameras were able to tell. They had some of the weapons manned. We also have aerial data that they were arming all of these weapons.”