It is hard to exaggerate the importance of the Iranian presidential elections, if Mahmoud Ahmadinejad is driven from power by Iran’s young, reformist voters.

What happens in Iran matters not only to its people, its neighbours and the wider Middle East but could have a profound impact on Western foreign policy and the presidency of Barack Obama.

When he came to power four years ago, Mr Ahmadinejad cleverly harnessed popular disillusionment with Tehran’s corrupt political establishment and anger at the way Iran was being treated by America. By then thousands of American troops were deployed along Iran’s borders in Afghanistan and Iraq. Some in Washington spoke openly of removing the regime in Tehran as they had done in Kabul and Baghdad.

In the space of a few short months, Mr Ahmadinejad called the West’s bluff. He pressed ahead with Iran’s controversial nuclear programme. He stepped up aid for militant groups such as Hamas and Hezbollah. He used every opportunity to challenge George Bush and mock his dying presidency. For that he made himself a champion across the Muslim world.

But Mr Ahmadinejad has now been outflanked both at home and abroad. He squandered Iran’s oil wealth and his handling of the economy has been little short of disastrous. His bizarre messianic beliefs have been openly ridiculed. Iranians, proud of their heritage and eager to be taken seriously, are growing increasingly embarrassed by their leader’s outbursts on the world stage. He has has repeatedly dismissed the Holocaust as a hoax, denied that there are homosexuals in Iran and hinted that he is on a mission from God.

Above all, Mr Ahmadinejad completely failed to adapt to the new political realities, ushered in by the arrival of President Obama.

When the US President offered a hand of peace to Iran, he was rebuffed. When he eloquently sought to build bridges with the Muslim world, Iran denounced his offer as a trick.

Millions of Iranians have now voted for Mir Hossein Mousavi, the main challenger for the presidency, whose sudden popularity is largely seen as a protest vote against Mr Ahmadinejad.

Under Iran’s constitution, the president is not the highest authority in the land. Real power — particularly control of foreign policy and the nuclear programme — resides with the Supreme Leader, Ayatollah Ali Khamenei. The president is one voice among many in the decision-making process.

But that reality fails to reflect the emotional nature of this election. If he is ousted from power, Mr Ahmadinejad’s removal could be a watershed in Iranian history. Even if Iran changes course by only a few degrees, it could open many opportunities. Iran and the West share many important goals — the need to keep the Taleban out of power in Afghanistan, the importance of democratic government in Iraq and the fight against narcotics, to name a few.

A softening of Tehran’s position could go a long way to undermine the cause of militant groups in the Middle East and even head off the threat of an Israeli military strike against Iran’s nuclear facilities.

The big prize lies in the so-called “grand bargain” that would see Washington and Tehran end their 30 years of hostility and Iran readmitted to the community of nations.

For that reason, it is not only young Iranian voters who are hoping for a change when the results from the elections come through this weekend.

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