BRASILIA (Reuters) - Brazil's ruling Workers Party, reeling from a humiliating defeat in an impeachment vote in Congress, is threatening to bring the country to a standstill with mass protests against what it calls a 'coup' to topple President Dilma Rousseff.
Party leaders' pledges to take their fight to the streets, after the lower house on Sunday backed a motion to impeach Rousseff, have raised fears they will attempt to destabilize a transitional government in Latin America's largest economy.
But the party's popularity has been shattered by a deep recession and a succession of graft scandals during its 13-year rule. It is a shadow of the organization that once commanded near fanatical support among Brazil's poor, and will struggle to sustain its fight against impeachment, analysts say.
Protests are part of the Workers Party (PT) DNA. Born in the grim industrial belt that rings Sao Paulo, it emerged from a union-led pro-democracy movement in the twilight of Brazil's military dictatorship in the 1980s.
It slowly developed into a formidable political machine. Brazil's first working class national party has won four straight presidential elections since Luiz Inacio Lula da Silva's breakthrough in 2002.
Yet formerly-loyal labor unions and leftist social movements have distanced themselves from the unpopular Rousseff because of belt-tightening moves adopted last year in a failed bid to curb Brazil's runaway budget deficit.
Abandoned by many of its allies within Congress as the political crisis has deepened, the party's national decline could accelerate once it loses its grasp on power and control over government resources and jobs, analysts say.
It would automatically relinquish the presidency if, as expected, Rousseff is put on trial in the Senate next month for breaking budget rules. The reins of power would pass to Vice President Michel Temer, denounced as a 'traitor' by Workers Party leaders, who would see out her term until 2018 if Rousseff is found guilty.
Party insiders and other political sources in Brasilia say the PT would not be able to keep up protests for long.
"Support for the PT has deteriorated, the party is weak," said Marco Antonio Baratto, the bearded leader of the Landless Workers' Movement (MST), a long-time ally of the PT frustrated by its lack of leftist reforms while in government.
"If you go to the slums today to defend the government or Dilma, they chase you away."
Speaking at a rally in Brasilia on Saturday against impeachment, he made plain the PT could not rely on automatic support from his movement: "If the government does not represent the interests of the workers, it will have a problem with us."
Workers Party leader Rui Falcão on Tuesday repeated calls for members to take to the streets to oppose what he called a right-wing conspiracy to roll back social benefits won by Brazil's poor since Lula took office in 2003.
"The PT will not give a possible Temer government any peace," he said at a news conference in Sao Paulo, with party founder Lula at his side. "Our opposition will go far beyond Congress. We are telling society that an illegitimate government will have no peace, there will be a fight."
The rhetoric of class-struggle has resonated with some grass-roots supporters.
"We'll go to the streets, we'll fight, because it's the only weapon we've got," said Jose Lacerda, 50, holding a red cap in his hands, standing outside Brazil's Congress building after Sunday's vote.
But many Brazilians blame the Workers Party's economic stewardship for worsening the deepest recession since the 1930s, which has thrown millions out of work and pushed unemployment to more than 10 percent of the workforce.
That in turn has reduced the clout of the unions and the PT's sway among organized labor.
When Lula swept to power as Brazil's first working class president, voters celebrated his pledges to clean up Brazil's corrupt and fragmented political system.
But PT involvement at the heart of a massive graft scheme designed to systematically milk political kickbacks from suppliers to state controlled Petroleo Brasileiro has shocked Brazilians used to decades of corruption scandals.
Leading figures from the PT have been jailed, including former party Treasurer Joao Vaccari Neto, who was sentenced to 15 years in prison in September.
Lula himself is being investigated for allegedly receiving a luxury seaside penthouse and a country estate from companies implicated in the graft investigation.
While he remains Brazil's most influential politician, Lula's prestige and influence has been badly dented by the scandal. Weariness with the PT has grown even among working class Brazilians, who have little appetite for a fight amid the dire economic situation.
"Lula will not be able to maintain pressure from the streets for very long because he is losing face with Brazilians, and the protests would further damage his credibility," said Thiago de Aragao at Brasilia-based consultancy Arko Advice.
As Sunday's impeachment vote ended in Rousseff's defeat, hundreds of PT supporters sat downcast on red flags and banners.
"The party won't recover from this loss," said Renato Bonetti, a social activist who traveled for 30 hours from the state of Parana in Brazil's south to march against impeachment.
"I'm not even sure I'll vote for them next election."
Reporting by Alonso Soto and Stephen Eisenhammer; Writing by Anthony Boadle; Editing by Daniel Flynn and Andrew Hay