As he surveys the aftermath of the rioting in Tehran, Ayatollah Ali Khamenei will be assessing the crisis he faces. Referring the complaints from defeated presidential candidates for a ten-day enquiry — just 48 hours after detecting a divine hand in the result — may stymie protests and gain time.

But the deeper challenge facing Iran’s supreme leader is to assuage or break up a coalition against Mr Ahmadinejad that has taken shape since the first year of his presidency. The events of the past week have widened the division between the president and his opponents, making it harder for Ayatollah Khamenei to defuse the situation through finding common ground.

The anti-Ahmadinejad coalition began in 2006 as a group of reformists and pragmatic conservatives alarmed at the new president’s foreign policy pronouncements, which they felt imperiled Iran’s international position. The group was also concerned at the president’s reflationary economics — and the harm inflicted on businesses by tougher western sanctions they blamed in part on Mr Ahmadinejad’s bellicose approach.

The three co-ordinators of this group were Akbar Hashemi Rafsanjani, the revolutionary veteran who holds important state positions, Mohammad Khatami, the former reformist president, and Mehdi Karrubi, the former parliamentary speaker.

But the “coalition of the concerned,” a term first used at the end of 2006, helped shape a wider political agenda. As June’s presidential election approached, many leading political figures, including Ali Larijani, the parliamentary speaker, and Mohsen Rezaei, former commander of the Revolutionary Guards, called for a government of national unity. Mr Rezaei even challenged Mr Ahmadinejad in the presidential election. As the election approached, Iran’s reformists displayed rare political acumen, agreeing to run Mir Hossein Mousavi rather than Mr Khatami, a move that made it far harder to Mr Ahmadinejad to exploit fears that the reformists masked radical, pro-western elements wanting to overthrow the Islamic system.

Harder, but not impossible.

Mr Musavi’s stress on “principles” during the recent election marked his centrist convergence. But his rallies, allied by the western media’s infatuation with Tehran and 20-year-old women with blonde highlights, began to resemble the radical student protests of the time of Khatami’s presidency. The so-called “green revolution” had all the connotations that fundamentalists abhorred.

Relishing the challenge, Mr Ahmadinejad met it head on.

Returning to the theme of his 2005 victory, he attacked Mr Mousavi as part of the clique of Mr Rafsanjani. As a humble man of the people, the sitting president would remain steadfast against those believed to have enriched themselves at the people’s expense: it was a message with resonance among parts of Iran ignored by the western media.

For Ayatollah Khamenei, events have emphasized just what a mixed blessing Ahmadinejad has been, and remains. On one hand, his victory in 2005 showed the egalitarian slogans of the 1979 revolution could still motivate the masses and rewrite an agenda dividing Iran between “reformists” and “conservatives.”

But this was far from all the Ahmadinejad story. The “popular president,” an outsider of humble background, has shown scant respect for Iran’s clerical and political establishment. His call for class struggle, albeit with an Islamic hue, attacks on an “oil mafia” and his posture as the international leader of have-nots against big powers, all carry the danger of instability and threaten vested interests developed since the 1979 revolution.

And his international stance — although popular with many ordinary folk throughout the Islamic world — has brought Iran growing western pressure. Tehran’s pragmatic conservatives and professional diplomats believe that cold decisions about compromise lie ahead and fear that Ahmadinejad generates far too much heat.

So where does it go from here?

The unifying factor among the “coalition of the concerned” has been a desire to see Ahmadinejad out of office, and that desire is now stronger than ever and likely to keep the coalition together at least for now.

Mr Mousavi has played a careful hand in supporting the protests in Tehran while condemning violence. He has demanded the recounting of the election, or perhaps a re-run. Mr Khatami has backed him.

The calculations facing Mr Rafsanjani are more complex. Unlike the reformists, he holds important state positions as head of the Expediency Council and the Experts Assembly. But it seems far too early for him to make a real move.

Ayatollah Khamenei and Mr Rafsanjani have worked together for nearly half a century, as revolutionaries, as leaders during the desperate war with Iraq, and as leaders of the Iranian state. But there is also rivalry between them, expressed in the belief in important places that Mr Rafsanjani, although five years the senior of the two, has not given up hope of exercising the powers of the supreme office.

Ayatollah Khamenei has always favoured a leadership style that keeps him, as far as possible, above factional politics. The coalition now facing him, including Mr Rafsanjani, is making it more and more difficult for him to do that.

A possible, and perhaps telling, move for Ayatollah Khamenei would be an attempt to woo Mr Rafsanjani and perhaps some moderate reformists away from the coalition opposing Mr Ahmadinejad.

But the election and the street rioting put Mr Ahmadinejad in a stronger position to deter any concessions, even ones designed to split his opponents. Meanwhile on the other side, the price Mr Rafsanjani and others might ask is surely rising by the day.

The situation is delicate. But of all the politicians weighing up their bottom line and their next move, Ayatollah Khamenei has the greatest onus to act — and to act decisively.