Even in the most ruthless years after the revolution, the associates and heirs of Khomeini never quite let go of the idea of a state that would be both Islamic and democratic. Most of the excluded reformists remain believers in the possibility of reconciling the two, rather than secular politicians in waiting. Whether Iranians share their beliefs or not, it was the reformists' participation in government that gave the Islamic republic some broad legitimacy. That legitimacy has been draining away for a long time, partly because the reformists in office proved ill-organised, divided and indecisive, and partly because Iranian expectations of political and economic improvement were too high. Above all, it has been because the reformists' attempts to curtail the role of the unelected conservatives - who control the judiciary and security forces, discipline the press and vet candidates for office - have been unsuccessful.

The revolution shared out power between two sets of institutions, the pinnacle of one being the democratically elected presidency. The other was headed by a "supreme leader", whose function was to act as spiritual guide to the nation and take final decisions when necessary, with an appointed council of guardians below him. The uneasy relationship of the two orders, one dominated by conservatives and the other, in recent years, by reformists, rested on an implicit bargain. The conservatives needed the popular support the reformists brought, the reformists needed the steel of conservative resolve to prevent the changes they wanted sending Iran down the slippery slope toward a secular state. Though both agreed there was a line that should not be crossed, they could not agree where it lay. The result was the abortive politics of recent years. Much was ventured, but conservative vetoes meant nothing was gained. Ayatollah Ali Khamenei, the supreme leader, seemed more the captive of the conservatives than their chief, and consistently failed to maintain a balance between the forces.

Iranians lost patience. The once popular Khatami is now much reviled, the radical student movement has parted company from the parliamentary reformists, and in the municipal elections a year ago the turnout was less than 30%. Meanwhile, many in both the conservative and reformist ranks continued using their positions to gain wealth and advantage, adding to popular disillusion.

At this point, the conservatives appear to have decided that the reformists had outlived their usefulness. In vetting the list of candidates for parliamentary elections, they ran the red pencil through 3,600 names of would-be candidates, almost all of them reformists, including 87 sitting MPs and a number of leaders of different reformist factions. The council of guardians later reinstated about 1,000 marginal candidates but would not give way on the more important names, including the MPs. As a consequence, almost half of the parliament has resigned, almost all reformist groupings are boycotting the elections, and provincial governors have said they will not help organise the voting - leaving open the possibility that the polls will be run and controlled by the revolutionary guard.

Khatami has so far not carried out a pledge to resign if elections were not free and fair, but he could do so in the days remaining before the vote next Friday, or afterwards. It is hard to see any outcome that will not deepen the crisis. It is possible that the elections might still be postponed, as the reformists have asked, but the conservatives would resist handing such a victory to their opponents. Otherwise, Iran will soon have a parliament and a president - either a discredited Khatami, if he stays, or a successor - with only minority support.

That would be a dramatic illustration of the way in which Iranian society and the political system have diverged to the point of divorce, as well as a tragedy for those who believe Islam and democracy can be reconciled. However, chaos might not be immediately around the corner. The older generation, although disillusioned and angry, has experienced the pain of one revolution, and is not anxious to embrace another.

Against that, there is the mass of young people who have grown up since the revolution, many of them living in a kind of "American dream", in which the US has become a totem representing the economic prosperity, personal freedoms and all other good things that are supposed to magically materialise if there is a change of regime.

Iran's political crisis has come at a time when its international isolation is diminishing. In spite of questions over Iranian sincerity on nuclear matters, seen again yesterday in Vienna, a certain convergence of US and Iranian interests is evident. American problems in Iraq and Afghanistan mean that Washington needs Tehran even more than it did before. Straws in the wind included a speech last year by Richard Armitage, the assistant secretary of state, saying, "it is not up to the US to choose Iran's future"; the American reaction to the Bam earthquake; a visit to Tehran this month by Congressional staff members; and, on the European side, visits by Javier Solana and Prince Charles. Iran, in other words, may be slipping off the axis of evil and on to the end of the axis of cooperation, although clear violation of recent pledges on nuclear weapons could send it spinning back again.

There is thus a possibility, to put it no higher, of some kind of Iranian-American rapprochement, with understandings touching on Iraq, weapons of mass destruction, trade, and even Palestine. Iranian conservatives and American neo-conservatives might well balk. But the Tehran conservatives certainly know how popular such a bargain would be at home, because of the nimbus that surrounds America for many Iranians. The jobs and investment that might follow would also be welcome. It could give a wholly conservative new government some desperately needed political credit. What an irony, however, that - if such a bargain is struck - it will not be with the transformed regime many inside and outside Iran once hoped the reformists would eventually create, but with a rump republic that has discarded its democratic aspirations.