There’s electricity in the air in Tehran. Beneath the snow-capped peaksthat tower over the city, crowds gather every night to argue in the streets. Campaign posters touting candidates in the June 12 vote cover the city. A year ago, when I visited Tehran in advance of the parliamentary elections, there was apathy. Voters then were convinced that their votes didn’t matter, and that not voting was the best way to protest the current state of affairs. No longer. There’s a wave building, and all signs point to a resounding victory for Mir Hossein Mousavi, the pro-reform candidate who is challenging President Ahmadinejad.

That wave is green. All over the capital, there are green signs and banners supporting Mousavi. Cars flying green flags speed through the city, honking horns for Mousavi. For years, the hardline clergy and their allies, including Ahmadinejad, have feared nothing more than an Iranian-style “color-revolution.” Now, Mousavi–with solid establishment credentials, an Islamic revolutionary pedigree second to none, and an outspoken pro-reform message–finds himself at the head of a green parade.

Of course, the hardliners and Ahmadinejad have a lot of aces up their sleeve, including the security services, the judiciary, the Revolutionary Guard, and the interior ministry, which counts the votes.

On Saturday, my first day in Tehran, I traveled some 25 miles outside the capital to Karaj, a city of three million people, for a rally for Mousavi at a huge soccer stadium. The scene was frenzied with excitement. At least 20,000 people waving green flags and dressed in green scarves packed the place. They did the wave. The cheers were deafening, and Mousavi hadn’t even arrived yet. In the VIP section, I ran into an Iranian Olympic wrestling champion, Ebrahim Javadi, who’d come to show his support. “I am sure Mr. Mousavi can help us survive this crisis,” he said. And better relations with the United States? “One hundred percent!” he said. Nearby, a middle-aged mullah, dressed in brown robes and white turban, said he’d watched President Obama’s speech. Akbar Hamidi, 48, is a specialist in Persian literature. “Please take our message of peace to America,” he told me. “I hope we elect Mousavi so he can start negotiations with the United States.”

When Mousavi entered, the frenzy hit new highs. A roar went up. People chanted: “If there is no election cheating, you are Number One!” and “Ahmadinejad, shame on you! Let’s get rid of you!”

And then: the power went out. Mousavi could not speak. He waved to the vast crowd, and they waved back. After half an hour, he waved goodbye. Rumors flew that someone–the most often mentioned culprit was the Basij, the paramilitary force that supports Ahmadinejad–had sabotaged the rally. Just another day of politics in Iran. The next day, another Mousavai rally was canceled at a stadium north of Tehran when the stadium management informed Mousavi staff that the rally would damage the playing field in advance of a match next week.”Just an excuse,” said an Iranian observer.

Later that night, more than 300 Iranian artists–painters, sculptors and others–convened an extraordinary gathering in support of Mousavi, whose outspoken wife is also an artist and who, in a step unprecedented in Iran, campaigns side by side with him, even holding hands. Hundreds of people gathered at the Gallery Mellat, and in an auditorium they listened to a speech by former President Khatami, the reformist, who is supporting Mousavi. “The government,” said Khatami, “has turned being anti-art into an art form.” Mousavi, who was prime minister from 1981-1989, had garnered across-the-board support from Iran’s intellectual community, including writers, artists, musicians, actors, and others. At the event I spoke to many world famous Iranian artists, each of whom said that each and every work they produce must be cleared by the Ministry of Culture and Islamic Guidance. And there was enormous buzz about Obama’s opening to Iran. “People hope we can find a new way with Obama,” said Farah Ossouli, who helped to organize the artists’ exhibition. “But if Ahmadinejad stays, we are not sure he wants relations with the United States.”

The next day, at Mousavi headquarters, I met Mostafa Hassani, 27, the whiz kid who came up with the idea of using green. It’s a concept that Hassani, a prize-winning design student, came up with in 2008, even before he knew who’d be running. “I wanted something that could unite the country. We decided on green. Everyone can have access to something green, and when you make something common, like a logo, people can adopt it.” He brought the idea to the Mousavi campaign a few weeks ago, and it clicked. He started with green arm bands, and it’s expanded. The latest innovation is a green-paint handprint and a green checkmate, for a vote. “People can slap their hands on the wall, even in remote areas.”

It’s a long and difficult climb for Mousavi, of course. But everywhere, it seems, support for Ahmadinejad is lackluster, and the Mousavi green wave is growing. The campaign, including an unprecedented series of TV debates, is growing bitter. Today, I’m going to a rally for Ahmadinejad, the former mayor of Tehran, in the center of the city. Stay tuned.