A year ago this month an estimated one million people poured onto the streets of Tehran. Those crowds - bazaari traders and academics, young and old, conservative pragmatist and fractious liberal - were drawn together by outrage over what they called a stolen presidential election: the incumbent president, Mahmoud Ahmadinejad, had been returned via ballot box numbers that appeared then, as they do today, fraudulent. The opposition candidate Mir-Hossein Mousavi told supporters that he had been cheated out of power.
It was, from the start, an impressive outpouring of political feeling. But amid a continued and vast street presence in the days following the June 12 election those crowds seemed to become something more: an embryonic movement that coalesced around 30 years of disillusionment and anger at the Islamic Republic and which now insisted on a new democratic politics, a liberalised society, and the primacy of human rights.
The loose alliance known as the Green Movement constitutes the most significant development in Iran's politics since 1979. One year on, then, it is time to ask three questions. What is the state of the Green Movement today? Does it have any chance of getting what it wants? And how should the rest of the world - in particular the US - respond to it? First, it's clear that the Green Movement - and the entire domestic situation - has altered since those few, heady days in June 2009. Any significant Green street presence has been extinguished: in particular, much was made earlier this year of the government's successful prevention of marches planned for the February anniversary of the Islamic Revolution. But as the British-Iranian historian Ali Ansari has pointed out, that success hardly constitutes the all-consuming victory that some observers saw at the time. The anniversary celebrations are a symbolic high point in the Islamic Republic's calendar of domestic propaganda.
This year, the government had to deploy an extensive Basij militia presence simply to mark that day without the embarrassment of vocal dissent. Here is recent, indirect proof, then, that the Green Movement remains extant. But in the face of the Republic's response, it has had to adapt. Let's not forget, meanwhile, the nature of that response. During the June protests Revolutionary Guardsmen fired on crowds with live ammunition. An estimated 200 were arrested, and Amnesty International reported 115 executions of prisoners in the 50 days after polling day. One year on, harassment continues: witness the recent incarceration of the director Jafar Panahi, held for three months on suspicion of plans to make a pro-Green film.
Given a regime that will go to these lengths, does the Green Movement have any realistic chance of effecting change? The answer is yes, if it can press its true advantages and play a strategic long game. And there's evidence that it is doing just that. So what constitutes the Green Movement's real advantage? The journalist and Iran watcher Hooman Majd has argued persuasively that it is best characterised not as a political revolution, but a civil rights movement. The Canadian-Iranian intellectual Ramin Jahanbegloo, a professor of political science at the University of Toronto, has also argued that the movement's importance inheres in its potential to spread a new conception of Iranian civil society.
More specifically, the Green Movement is an alliance of political grievance that brings together the historically troublesome, educated, disaffected youth of north Tehran with disillusioned members of Iran's revolutionary generation: reformist politicians such as Mr Mousavi and fellow 2009 presidential candidate Mehdi Karoubi, disappointed by the regime's failure to deliver the social justice that it promised. Mainstream Greens, then - and certainly leading voices, such as Mr Mousavi's - do not support wholesale overthrow of the Islamic Republic, but evolution from within. Crucially, to retain this broad-spectrum political support - and avoid alienating the many ordinary Iranians who have no appetite for another political convulsion - the movement must resist the inevitable pull towards violent radicalisation and embrace a civil rights approach broad enough to attract a majority of Iranians.
And it seems that it is doing this: at demonstrations during Ashura, mainstream Greens prevented radical members from attacking security forces. When Mr Mousavi re-stated Green aims this January, he dropped a demand for an annulment of the 2009 election result. Protest among younger, more militant Greens was limited. The second prong of a civil rights strategy must be the expansion of the movement beyond its base of middle-class, educated Tehranis. The Greens must cultivate a new conception of Iranian civic society - one based on respect for human rights, democratic politics, and transparent government - among ordinary Iranians, such that even natural Ahmadinejad supporters (the rural poor and urban working class) will never again tolerate near open election fraud and callous disregard for individual liberty.
Again, there are encouraging signs. In February, for example, Tehran's bus drivers' union declared solidarity with the Green Movement and called on Tehranis to take to their cars to cause traffic jams at 6pm each evening (though given the already mind-numbing density of Tehran evening traffic, it's hard to tell whether any took up the cause). Change by these means will be slow: the Iranian Green Movement is now engaged in a marathon, not a sprint. The last question becomes, then, how can foreign governments - in particular Washington - help to advance the cause? The key is a light and astute touch. Explicit US support for the Greens, of course, is not an option: that would only let Mr Ahmadinejad portray the movement as a foreign project in "soft" regime change. But playing hardball with the Islamic regime doesn't always help, either.
It's clear, first, that military action against Iran's nuclear plants would be the single best way to unite Iranians around Mr Ahmadinejad and his cartoon brand of high-pitched nationalism. Indeed, even the current diplomatic wrangling over the nuclear issue is an irritation to many ordinary Iranians, who sympathise with the leader when he says that Iran has a right to nuclear energy. Harsh economic sanctions are currently under the consideration of Western leaders, but should they hit the pockets of working Iranians Mr Ahmadinejad will sleep more soundly in his bed. When the US appears amenable to a fair deal on the nuclear issue, it indirectly bolsters Green aspirations.
Obama should save his hard words, instead, for the Islamic Republic's violations of human rights. By failing to condemn these violations as regularly, or vociferously, as he does supposed violations of the Nuclear Nonproliferation Treaty, he allows the impression among Iranians that the West cares little for them, and that the idea of "human rights" - an idea that the Green Movement must now weave into the fabric of the Iranian national conversation - is an empty one, trotted out by cynical Western leaders when it is useful and dropped when inconvenient.
Last, outside actors should do what they can to encourage the free flow of information in Iran. It's commonly known that the June 2009 protests were facilitated by online tools such as Twitter and Facebook. The regime now restricts internet access to known Green activists and slows the net to a crawl on potential flashpoint days. Software that can frustrate those efforts and empower Green activists, such as the encryption programme Haystack - custom-made in San Francisco, and licensed by the US government for export to Iran - should be given every possible encouragement.
The cause of Iranian civil rights will demand patience, acumen, and moral strength from those who serve it, whether inside or outside the country. But the prize in reach is of the highest kind: a free, just and stable Iran, restored to the dignity that its people deserve. David Mattin is a journalist and writer based in London. In 2009 he wrote and presented the BBC Radio 4 documentary The Flight from Tehran.