Italian Premier Romano Prodi resigned after his center-left coalition lost a Senate confidence vote, a humiliating end to a 20-month-old government plagued by infighting. Italy now faces the prospect of early elections or the formation of an interim government, a decision that must be made by President Giorgio Napolitano. Prodi will stay on in the meantime in a caretaker role. Elected in April 2006, Prodi had a shaky government from nearly the start. It lurched toward collapse this week after a small Christian Democrat party, whose votes were vital to his Senate majority, yanked its support in the latest coalition spat. The government lost 161-156 Thursday after a fiery debate during which one senator was spat upon, fainted and had to be carried out on a stretcher. Lawmakers from the conservative coalition of former Premier Berlusconi cheered and popped the cork on a bottle of sparkling wine as the defeat was announced. Berlusconi, the billionaire media magnate who lost to Prodi in 2006 and is eager to return to office, called for swift new elections. But some lawmakers are pushing for an interim government to reform an electoral system blamed for contributing to Italy's chronic political instability. Decades of revolving-door politics have produced 61 governments since World War II. It was the second time that Prodi was forced to resign because of betrayal by his allies. His first term as premier ended after two years in 1998 when he lost the support of the radical left. Italy's political climate stabilized in recent years, with Berlusconi's conservative government lasting for a full five-year term starting in 2001. But Prodi's coalition - ranging from pro-Vatican centrists to Communists and Greens - began to squabble soon after his victory over Berlusconi. Known for his unemotional speaking style, Prodi appealed to senators before the vote to let his government continue so it could carry out badly needed reforms. Among the changes would be an overhaul of an electoral system blamed for giving small parties disproportionate weight in fragile coalitions. Prodi, 68, had also pledged to reform Italy's costly pension system and boost growth by liberalizing many areas of Italy's economy, from insurance and banking services to taxis and pharmacies. But the reforms were often watered down after street protests or under pressure from the radical left in the coalition. Italy's economy, while emerging from a period of zero growth, remained sluggish. Other campaign promises remained unfulfilled, such as giving legal rights to same-sex couples, a bid which angered some centrists in his coalition. "The country leaves Prodi here and moves on, I don't see him as a meaning political figure in the future," said Franco Pavoncello, a political science professor at Rome's John Cabot University. On Wednesday, Prodi won a confidence vote in the lower Chamber of Deputies, where his coalition forces have a comfortable majority. He said he went through with the riskier Senate vote "not a gesture of stubbornness but of being consistent." But he lost his gamble that his allies might close ranks and that Italy's seven senators-for-life could rescue him as in the past. Berlusconi said his conservative lawmakers would veto any push for a "technocrat" government, an idea supported by lawmakers who want Parliament to enact reforms of the electoral system. "We need to go to the polls in the shortest time possible without delay," Berlusconi was quoted as saying by the Italian news agency ANSA. But the leader of the largest party in the government, Rome Mayor Walter Veltroni, contended that early elections would only "push the country into a situation of dramatic crisis." Veltroni, the head of a leftist group of former Communists and pro-Vatican centrists, is considered the likely candidate for the left. The presidential palace said Napolitano would start consulting with political leaders Friday on what to do next. During the debate, one senator, Christian Democrat Nuccio Cusumano, stood up after Prodi's speech to announce he was breaking with his party to vote in favor of the government. Some lawmakers from his UDEUR party - the group that defected from Prodi's coalition earlier this week - responded with calls of "traitor" that resounded through the Senate. Cusumano was spat upon, fainted, and was carried out on a stretcher. He returned to vote "yes" a few hours later.