Voters, in Midterm Elections, Give New Momentum to the Opposition in Argentina BUENOS AIRES - After a decade of family rule in Argentina, the political tenor has begun to change. Argentines voted in midterm elections on Sunday that gave new momentum to the opposition, most significantly in Buenos Aires Province, home to more than 15 million people in this nation of 40 million. The Renewal Front party, for which Sergio Massa, a municipal mayor, headed the list of candidates, won heavily here with almost 44 percent of the vote, 12 points ahead of President Cristina Fernández de Kirchner's party, the Front for Victory. Mr. Massa, 41, will lead a small bloc of 16 politicians in the lower house of Congress. He is also expected to start building up for a presidential bid in 2015 by gradually fracturing Mrs. Kirchner's Peronist support structure, though he faces the challenge of sustaining momentum over the next two years. "Massa has consolidated himself as a key player for 2015," said Carlos Germano, a political analyst. But the challenge starts now. The Constitution blocks Mrs. Kirchner - who succeeded her husband, Néstor Kirchner, as president in 2007 - from running for a third consecutive term. Some in her party had spoken publicly of an "eternal Cristina." But the Front for Victory was far from obtaining the two-thirds Congressional majority it needed to precipitate constitutional changes. At a downtown theater here on Sunday night, party officials celebrated winning 33 percent of the vote nationwide, more than any other party. But they also cut confused and forlorn figures. There is no clear successor to Mrs. Kirchner. Her husband, a popular figure who many expected to succeed her in a presidency-swapping strategy that could have extended the family's political dynasty, died unexpectedly in 2010. Mrs. Kirchner has overseen an expansion of social benefits, a liberal social agenda and a string of nationalizations. But discontent with her administration is widespread. Voters who accuse her of centralizing power say it is time for change. "This signals a clear beginning of the end for Kirchner rule," said Sergio Berensztein, a pollster and political commentator. Mr. Massa's campaign centered on tackling high inflation, which economists estimate at 25 percent, and violent street crime. "This government is letting us down," said Santiago Bauzá, 38, a painter who was voting in Tigre, the municipality where Mr. Massa is mayor. Massa can change our politics. He is progress. The rise of Mr. Massa and opposition figures in other pivotal provinces represents a "jump toward moderation," Mr. Berensztein said, after a decade of confrontation, particularly with the country's important agriculture sector, that has polarized Argentines. Mr. Massa told cheering supporters on Sunday night: "The people have spoken. And their message is clear. Mr. Massa was Mrs. Kirchner's chief of cabinet for a short period in 2008 and 2009, but he left her Peronist party in June to start the Renewal Front. Mr. Massa describes his party as having "a Peronist heart, but a modernist brain." Its proposals are widely viewed as business-friendly and a move to the center. Peronism has dominated Argentine politics for more than 60 years, but the movement has often splintered and its leaders do not occupy a fixed point on the political spectrum. Those who voted for Mrs. Kirchner's Front for Victory party fear that Mr. Massa will do little to help the poor, even though he has publicly supported some of Mrs. Kirchner's welfare programs. "When the frenzy subsides, we will see Massa's true colors," said Juárez Orlando, 58, a furniture mover from Tigre. His reign here has only benefited the rich. The Front for Victory lost 12 of 23 provinces, including major urban centers. It also came in third in the city of Buenos Aires, far behind the congressional candidates of Mayor Mauricio Macri's center-right party. Mr. Macri, a longtime opponent of Mrs. Kirchner, immediately announced that he would run for the presidency in 2015. In total, a third of seats in the Senate and a half in the Chamber of Deputies were up for election. Mrs. Kirchner, who is recovering after surgery on Oct. 8 to drain a blood clot near her brain, has maintained her slim majority in both houses, allowing her to "govern with calm," Mr. Germano said. Supporters of her political movement, known as Kirchnerismo, also pointed to her comeback from defeat in midterm elections four years ago. "When Kirchnerismo feels weak, it doesn't cave in," said Gerónimo Gorriarena, 24, celebrating here Sunday night. It redoubles its efforts.