It's just a two-sentence text message bouncing among young Iranian voters. But it carries some big hopes. It begins with a reminder of what happened four years ago: Many reformists boycotted presidential elections and opened the way for Mahmoud Ahmadinejad's underdog victory as president. It closes with a rallying cry for Friday's turnout: "Now, you and I vote so that he will be defeated." Whether that's possible is far from certain. But the brief text - blipping across tens of thousands of screens - is more important for its optimism than its analysis. There's a growing sense that Ahmadinejad may be vulnerable and Iran's highest elected office could shift back to more moderate hands with enormous stakes ahead. Among them: How Iran deals with Western fears about its nuclear program and responds to President Barack Obama's offer to ease a nearly 30-year diplomatic estrangement. If nothing else, the rising challenge from Ahmadinejad's main pro-reform rival, Mir Hossein Mousavi, has revitalized Iran's liberal voices after four years of being demoralized and in disarray - a problem that was partly self-inflicted. "I had lost faith in the ballot box and didn't vote in 2005," said Behnaz Pirasteh, a 20-something woman wearing a green ribbon that's become the symbolic color of Mousavi's campaign. "I want now to save my country from total destruction." No credible independent polling exists in Iran. So handicapping political races includes measuring street buzz and hints of shifting momentum. At the moment, many of the signs seem to be moving in favor of Mousavi, a graying elder statesman and amateur artist who served as Iran's prime minister during much of the 1980-88 war with Iraq. Just a few months ago, he was little more than a figure in a history book for many young voters. But he courted them with every tactic of a modern campaign: Facebook, blogs, side-by-side appearances with his charismatic wife and finding a hip gimmick with his "green movement" - T-shirts, bracelets, flags and even emerald-colored head scarves. At one rally, poet Eqbal Mansourian warmed up the crowd with verse: "Make our lives green again, make it rain again, make us hope again." Mousavi also has stayed on message. He has hammered Ahmadinejad on the irony of Iran's limping economy despite its oil and gas riches and ridiculed his bombastic style, such as questions about the Holocaust, as a recurring black eye for Iran's international image. Mousavi's much-repeated quip: Iranian passports now have the same status as Somalia's. In a rare, face-to-face debate Wednesday, broadcast live across Iran, Mousavi projected a steely calm as Ahmadinejad fidgeted and smirked. "Our nation's dignity has been harmed," Mousavi said. "We've been degraded." It's shrewd political theater. The Iranian self-image runs far deeper than the 1979 Islamic Revolution and its confrontations with the West, and is largely built upon the idea of pride in Persia's - and Iran's - place among the world's great civilizations. Mousavi, in essence, seeks to portray Ahmadinejad's government as a betrayal of what it means to be Iranian. "The green tsunami of change is on the way," read a headline Wednesday in Kalemeh Sabz, or Green Word, Mousavi's daily newspaper that hit newsstands last month. After the debate, street rallies dueled with slogans: Ahmadinejad's backers cried he was "our love" and Mousavi's supporters sang "Ahmadi-bye-bye." But Ahmadinejad will not be easy to sweep away. His man-of-the-people credentials are still strong and his government has lavished backers with handouts that include checks worth the equivalent of $100 - about a week's pay for a provincial government worker. He also has vast support among Iran's true leaders: the ruling clerics and their military wing known as the Revolutionary Guard. The president is Iran's political face to the world, but the theocrats are the real masters of the country's destiny. They dictate every important policy, decide who is worthy of running for office and can mobilize millions of votes with just a word. "Mousavi might be able to charm the voters, but it's not certain that he can pull an upset," said Ehsan Ahrari, a professor who follows regional affairs at the Asia-Pacific Center for Security Studies in Honolulu. The theocracy also controls the groups that hold elections and verify the count. Iran's elections - especially by Middle East standards - are considered generally fair. But no outside monitors are allowed, and reformers always hint at the possibilities of fraud in a close race. In 2005, rivals of Ahmadinejad complained bitterly of alleged vote rigging in his favor, but the charges were never investigated. The race this time is getting tighter and more tense. Predictions are growing that Friday's four-way election will end without a clear winner - gaining more than 50 percent of the vote - and force a run-off between Ahmadinejad and Mousavi on June 19. But that scenario hinges on a number of assumptions. The main one is that under-30s - about a third of the 46.2 million eligible voters - will turn out in large numbers for Mousavi and not stay on the sidelines as in 2005. It's also unknown how much votes will be siphoned off the two trailing candidates: former Revolutionary Guard commander Mohsen Rezaei drawing hard-liners, and moderate Mahdi Karroubi, a former parliament speaker and the only cleric in the race, pulling in liberals. "We can see frustration and fear" among Ahmadinejad's backers, said Mohammad Ali Abtahi, who served as vice president under reformist President Mohammad Khatami. For Khatami, the patriarch of Iran's liberal ranks, the campaign has been a chance at a political makeover. He ended his eight years in office in 2005 diminished and scorned in the eyes of many of his followers. He lacked the will to seriously challenge the limitless powers of the ruling clerics. And he failed to groom a successor with more stomach for a fight. Khatami entered this year's race briefly, but bowed out in March and has become a celebrity campaigner for Mousavi. His main mission: get out the youth vote in the same force that pushed him to victory in 1997 and 2001. "Nothing can stop (Mousavi) if there's a high turnout," Khatami told a rally last week. "You can replay 1997 and 2001." But Iranian elections are notoriously hard to predict. Few anticipated Khatami's first landslide 12 years ago. In 2005, Ahmadinejad was considered such a long shot that even his final campaign rallies were barely covered by Iranian reporters. The crucial - and impossible to measure - factor is what is being discussed at the very top: Whether Supreme Leader Ayatollah Ali Khamenei would consider trying to sway the vote Ahmadinejad's way now that it's a real race. Or, as American analyst Michael Hanna said, they could step back and let the chips fall, knowing that they still hold all the cards on major issues such as possible talks with Washington and Iran's backing for militant groups such as Hezbollah and Hamas. In the Middle East, every hint of possible changes in Iran's outlook is studied closely. Sunni Arab states are worried about expanding influence from Shiite Iran. Israel sees a clear threat from a nuclear-armed Iran - although Tehran says it only seeks peaceful reactors for energy. "Iran is really one of the few countries in the Middle East that really does have a civil society where the population can make a difference," said Gerald Steinberg, chairman of the political science department at Israel's Bar Ilan University. "The election of someone other than Ahmadinejad would signal that the Iranian public really does want a change away from confrontation ... If Ahmadinejad is re-elected, that will be a sign that nothing has changed and the clock is ticking and someone has to take strong action, either diplomatically or militarily."