Andrew Apostolou is a Senior Program Manager at Freedom House.

Today, Mir Hussein Mousavi organized a demonstration in which he reportedly turned out as many, if not more people, than he did for Monday's giant protest. His supporters mostly wore black and carried candles in a vigil that took them from southern Tehran to past Beyt-e Rahbari, the official residence of Ayatollah Ali Khamenei, Iran's theocratic leader.

As importantly, Mousavi personally attended the rally. Mousavi's people have been on Tehran's streets four straight days in a row, an important affirmation of the strength of the movement. By contrast, Ahmadinejad's supporters have only demonstrated once, in a state-organized rally in Tehran on Tuesday. Ahmadenijad himself did not attend--he was at an international summit in Russia--and the rally was later mocked after the main pro-regime newspaper, Keyhan, increased the numbers with the aid of Photoshop.

In Tehran, Mousavi has clearly done a better job than his rival of uniting his supporters and swaying international opinion. And as the turmoil stretches into its second week, there are two very important factors for the Greens to consider: First, the regime's security forces have been stretched. The number of protests across all of Iran has been impressive--outside of Tehran, there have been protests in in Sari, Tabriz, Isfahan, Kerman, and Rasht, to name just a few--and they have prevented the police from concentrating and crushing dissent as they did during the student uprising in Tehran in 1999 and the 1992 Mashhad riots. Although regime violence still seems to be continuing in the provinces, the scope of protests is making the security forces' job more difficult.

Second, though Mousavi has successfully increased pressure on the regime, tomorrow could be a turning point. Khamenei will lead Friday prayers at Tehran University. Regime supporters will be there in strength, with plenty of bussing to help pack the crowd. Two weeks ago at Friday prayers, Khamenei sat and watched as the regime-organized crowd shouted for Ahmadinejad.

While what Khamenei says tomorrow matters, how the crowds behave could have greater consequences. We know that Mousavi has been debating about how to respond. Mousavi initially wanted his people to ring the university and shout so that Khamenei could hear them. Mehdi Karrubi, his ally and fellow unsuccessful presidential election candidate, wants his people to attend and wear black. Then Mousavi changed his mind and told his people not to attend. He knows that this could lead to violence, which will discourage some of his supporters from demonstrating and dissuade others from joining him. In addition, the regime will accuse him of politicizing Friday prayers (which is the regime's prerogative). Many of Mousavi's supporters are highly conservative people who believe in the fundamental value of the Islamic Republic, but do not care for Ahmadinejad and his antics. Having them with him strengthens his hand. Losing them will marginalize him. He has now decided to hold his next march on Saturday, and he will be joined by former President Mohammad Khatami.

--Andrew Apostolou

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