Surrounded by a ring of mountains like a concert band shell, Beirut has great acoustics. So the roiling street battles on May 8 between Hizballah militiamen and supporters of the Lebanese government echoed through the city with a drumroll of rocket explosions and a chorus of machine-gun fire that sounded like the symphonic overture to civil war. When an early-summer thunderstorm began that night, it seemed as if the heavens themselves were taking up the ominous theme.But by the next morning, the battle for Beirut was mostly over. After just six hours of all-out fighting, Hizballah militants were in control of areas of West Beirut that had previously been the government's preserve. This made for some incongruous scenes. Bearded men with rifles and rocket launchers secured lingerie shops and a Starbucks in the commercial Hamra district. Elsewhere, they surrounded the houses of ministers and members of Parliament and watched buses evacuate students from the American University of Beirut. "It was like a field trip for us," said a Hizballah fighter standing on the Corniche, the city's seaside promenade. "Some [government loyalists] were begging us not to kill them. They were literally pissing in their pants."Hizballah's victory was hardly a surprise. Its Shi'ite militiamen, who number in the thousands and are armed by Syria and Iran, have survived battle with the mighty Israeli army, while the supporters of Prime Minister Fouad Siniora's government are poorly armed amateurs on neighborhood patrol. Neither the police nor the military — which has received hundreds of millions of dollars in arms and training from the U.S. — dared to lift a finger against Hizballah. Long after the militiamen had withdrawn from the streets, the army said it would intervene in any ongoing clashes but added that it would not disarm Hizballah.Despite the backing of the U.S., Western Europe and Arab states like Saudi Arabia, Siniora barely clings to power from his official residence and office in the Grand Serail, a former Turkish fortress surrounded by rings of barbed wire and riot police. But it is Hizballah's fire-breathing leader, Sheik Hassan Nasrallah, who's calling the shots.Sounds familiar? Think of Iraq, where a U.S.-backed government is bunkered down in the Green Zone, fighting fitfully against Shi'ite militias. Or of Palestine, where despite U.S. support and aid, President Mahmoud Abbas is powerless against the Iran-backed Hamas in Gaza. When dealing with internecine Arab conflict, the Bush Administration has never been able to back the winning team; it invariably attaches unrealistic expectations to moderate parties and underestimates extremist groups. The lesson, says Bilal Saab, a Lebanon expert at the Brookings Institution, is that "you can't pick sides in a civil war."Power Without ResponsibilityNasrallah unleashed his fighters on the streets of Beirut after the government tried to shut down Hizballah's private telecommunications network. But he has been spoiling for this fight since November 2006, when Shi'ite parties walked out of Siniora's coalition Cabinet. Although Lebanon is a democracy, the legitimacy of its government depends on a system of sectarian quotas; without the Shi'ites — the country's largest, fastest-growing group — the Prime Minister, a Sunni, has lacked both validity and street cred. The Shi'ites' price for returning: a greater share of power, including the right to veto major decisions. Siniora and other pro-U.S. members of his coalition have thus far refused, fearing among other things that such power would legitimize Hizballah's status as a state within a state.That train has left the station. The speed and ease with which Nasrallah's fighters took over Beirut — and the military's reluctance to stop them — suggest that Hizballah has free rein of the country. Unlike Hamas, which is confined to poverty-stricken Gaza, Hizballah has at its disposal an entire country, complete with a sophisticated banking system, an international airport and a friendly neighbor in Syria. Never has a terrorist organization had that kind of infrastructure. Saab notes that Hizballah's leaders can now have their cake and eat it too: "They're in control in Lebanon without having to actually run the state."This is all very bad news for Israel, which was drawn into a war with Hizb-allah in 2006 that cost 1,600 lives, mainly on the Lebanese side. "Lebanon," says Israeli Vice Premier Haim Ramon, "is controlled by this terrorist organization, and its government has become irrelevant." Israelis point out that behind Nasrallah and his fighters lurks a possibly greater threat: Iran. Hizballah's dominance in Beirut allows Tehran to project its power into the Mediterranean Sea, something the U.S. and its European allies must now factor into their calculations. (The Pentagon denied reports that the U.S.S. Cole, heading to the Mediterranean from the Persian Gulf, was responding to the Lebanon crisis.)The Bush Administration's response has consisted largely of hand-wringing. President George W. Bush blamed Iran for backing Hizballah, while Secretary of State Condoleezza Rice congratulated the Arab League for issuing a statement rejecting the use of violence in Lebanon. In truth, not for the first time in the Middle East, the Administration finds itself short of good options. It can no longer count on Siniora and the Lebanese security forces to halt Hizballah's growing strength. The only way to achieve that, says Saab, is to press Israel to give up disputed territory it seized in 1967. "It removes the pretext Hizballah has for its weapons," he says.But Israel has given no indication it will make any such concession, and few in Lebanon expect Nasrallah and his militia to weaken anytime soon. That's why some U.S. allies in Siniora's government believe it's better to engage Hizballah than pretend it can be crushed. On May 11, Walid Jumblatt, one of the leaders of the governing coalition, placed a call to Nabih Berri, the speaker of Parliament and a Hizballah ally, while TIME waited nearby for an interview. "Tell [Nasrallah] I lost the battle and he wins," Jumblatt said. "So let's sit and talk to reach a compromise. All that I ask is your protection."As the hereditary chieftain of Lebanon's Druze Muslim minority, Jumblatt earned the nickname "the Weather Vane" for being able to steer his followers through the ever changing winds of Middle Eastern politics. A former vassal to the Syrian regime, he switched his loyalties to the Bush Administration after the invasion of Iraq, when it briefly seemed as if American military power would transform the region. Now he seems ready to turn again. Sitting in his garden terrace with a few family members and loyal retainers, Jumblatt said that he has spoken with the U.S. embassy to deliver his grim assessment. "The U.S. has failed in Lebanon," he said. "We have to wait and see the new rules which Hizballah, Syria and Iran will set. They can do what they want."Brian Bennett/Washington and Tim McGirk/Jerusalem