Just getting thousands of protesters into the streets of Tehran despite fears of beating and arrest was a victory for the Iranian opposition, but the first protest in nearly two weeks also displayed the movement's limitations. Iran's clerical rulers are betting that with no clear leader and security forces bearing down, such dramatic shows of discontent will be hard to sustain. What the thousands of mainly young men and women marching Thursday did have going for them was determination. When security forces charged, beating them with batons, protesters scattered, regrouped nearby and resumed their chants of “death to the dictator.” They pumped their fists or flashed victory signs in the air, dashing for cover when police fired clouds of tear gas. One witness account posted on line Friday described a girl shoving a police officer who grabbed her then punching him in the stomach before escaping. Protesters blocked roads with chunks of concrete, trying to stop the motorcycles of the feared Basiji militiamen from reaching the crowds. There were also signs of support from those who didn't join in. Amid the turmoil, shopkeepers and residents let fleeing protesters slip into their homes or shops. Notably missing, however, was the man whose name many of the demonstrators chanted: Mir Hossein Mousavi, the pro-reform candidate they say was cheated of victory in the elections by vote fraud. Mousavi and other mainstream reform politicians appear to have had little role in organizing the demonstrations. Mousavi in part may have feared arrest if he came out in support of more street demonstrations. But he has also given signals the past week that the time for protests has past, hinting he could start a political party to press his demands for change within the system. The election dispute has demonstrated that many Iranians are unhappy with their government – but there is no consensus on how to harness that anger and to what end. Mousavi and most pro-reform leaders see the protests as leverage against the clerical leadership and hard-line President Mahmoud Ahmadinejad, but they don't want anger on the streets to get out of control, he said. “They don't want to press things too far. They don't want to bring down the system,” Nader said. As a result, Thursday's marches were largely inspired by young activists and students using the Internet to get the word out. They were able to make a startlingly strong showing with such informal methods – but doing so consistently at a time when activists are being arrested may prove difficult. The protests that erupted in the weeks immediately following the election were far larger, with hundreds of thousands from all levels of society filling Tehran's broad avenues. In the days that followed, raids snatched up more activists, journalists, bloggers and pro-reform politicians. The number arrested Thursday is not known. Also arrested was an Iranian-American scholar, Kian Tajbakjsh, who was seized by police from his home late Thursday, according to a relative in the United States who is in touch with Tajbakhsh's wife. Tajbakhsh was arrested in 2007 and spent four months in prison on suspicion of fomenting unrest in Iran. Still, despite the scenes of mayhem Thursday, security forces stopped short of the all-out assault that some authorities had promised. Police are likely wary of causing deaths that would spark a backlash and more of the public into the streets. A leading cleric delivering Tehran's main prayer sermon on Friday took a soft tone, saying all those who voted in the election were “brothers and sisters” – but underlining that it was time for the opposition to drop its campaign. “In most countries, defeated candidates do not continue their objections after the election. Those who do no not win should not pursue the issues any longer,” Ayatollah Mohammed Imam Kashani told worshippers at Tehran University, where a day before protesters marched on the gates, blocked by lines of riot police.