Let's get this straight: The people who will change Iran for the better are the Iranians. A U.S. president's words at the United Nations General Assembly can't do that. European talks and sanctions can't do that. Israeli bombs on Iranian nuclear installations certainly won't do that. But the Iranian people - yes, they can.
This is what millions of Iranians set out to do, in mass demonstrations this summer, and that is what some of them are still trying to do, despite beatings, killings, torture, rape, arrests and a grotesque show trial of leading reformists.
There are acute limits to what democracies and democrats outside Iran can do to help the "green movement" directly, but the first policy imperative must be to do nothing that makes their struggle more difficult. Be Hippocratic: First, do no harm.
Mr. Obama is right to instruct his officials to negotiate without preconditions on the nuclear issue. Washington should have done that long ago. But European powers have been negotiating with Tehran for years. While stringing them along, the Islamic Republic has been spinning ever more centrifuges - bringing itself closer to the threshold where it can decide whether to go for a nuclear weapon.
Negotiations should continue. But for the sake of a few more slippery promises of nuclear restraint, the United States and Europe must not give more legitimacy to a fraudulently elected leader, Mahmoud Ahmadinejad, who celebrated Jerusalem Day last week by saying that the "pretext" for the creation of Israel - the Holocaust - is "a lie based on an unprovable and mythical claim."
A textbook example of what democracies should not do was provided last year by a joint venture between Siemens and Nokia, which sold the Iranian regime a sophisticated system that can monitor the Internet, including e-mail, phone conversations and social networking sites such as Facebook and Twitter, much used by Iranian protesters. In the modern politics of people power, that is the equivalent of selling tanks or poison gas to a dictator. So, to be clear: A German company that used slave labour during the Third Reich sold a Holocaust-denying President the instruments for persecuting young Iranians risking their lives for freedom. Think of that every time you buy something made by Siemens.
Analysts who study Iran sometimes use the image of a race between the nuclear clock and the democracy clock. The regime has the nuclear clock ticking faster than many in the West anticipated, but the people have also now set the democracy clock going in a way most Western diplomats never believed they would.
This is not just a bunch of angry young people with green headbands. The Islamic regime is divided at the very top, and the Supreme Leader's authority is being questioned as never before. Pillars of the Islamic establishment, such as Ayatollah Hashemi Rafsanjani, are locked in conflict with Mr. Ahmadinejad and the Revolutionary Guards, who currently have the Supreme Leader's ear.
The phrase "democracy clock" is perhaps misleading. Iran is not going to be a full Western-style liberal democracy any time soon. What is still possible, however, is a mix of reform and revolution - what I have called "refolution" - that strengthens the constitutional republican elements in Iran's strange hybrid system and weakens the Islamist revolutionary ones. At the moment, the opposite is happening.
By throwing his theocratic authority behind Mr. Ahmadinejad and the Revolutionary Guards, Ayatollah Ali Khamenei has tipped the scales toward the revolutionary side. The best likely outcome of a "negotiated revolution" would be a decisive tipping of the scales in the other direction.
This would be a better Iran for the Iranians, but for the rest of the world? Skeptics say there is little evidence that reformists would be any less militant on the nuclear issue. A spokesman for the green movement, Mohsen Makhmalbaf, issued a statement Tuesday saying "the Iranian green movement does not want a nuclear bomb." Opposition leaders could usefully get more specific: for example, accepting the idea of neutral international supervision of the fuel cycle in a civilian nuclear program, on the clear understanding that this would apply to all civil nuclear powers, including the United States.
There are, I say again, severe limits to what democracies - especially the United States and Britain - can do directly to promote political change inside Iran. All the more important to do the indirect things better. One thing London has done is to fund the first-rate BBC Persian television and Internet service, which in less than a year has become an indispensable source of news for Iranians.
But too-direct support for the opposition will only give credibility to claims that the reformists and green movement are tools of a foreign plot - claims that have some traction with public opinion, partly because there really was a British-U.S. plot to topple prime minister Mohammad Mossadeq half a century ago. Mr. Obama may have been too hands-off in his reaction to the summer protests, but it was a matter of a few degrees of calibration. At the UN this week, he spoke of "the rights of people everywhere to determine their own destiny." Exactly so.
So we must not give any legitimacy to an illegitimate, Holocaust-denying President, for the sake of nuclear negotiations that have not yet gone anywhere. We should not put all our money on the democracy card, but nor should we put it all on the nuclear negotiation card. Every diplomatic move we make should be scrutinized for possible impact on the fissile political process inside Iran.
It may be that in a year's time, we have to acknowledge that the refolution in Iran really has been repressed, at least for now. In that case, we would have to deal as best we could - by negotiation, pressure and containment - with Mr. Ahmadinejad and an Islamist revolutionary regime. But that time is not yet. The contest is far from over. Its outcome is not up to us, but at least we must do nothing that helps the wrong side win.
Timothy Garton Ash is senior fellow at Stanford University's Hoover Institution.