Even the revered former president Luiz Inácio Lula da Silva – Lula – has been dragged into a long-running corruption probe that is dividing Brazilians

Brazil’s president, Dilma Rousseff, is fighting for her political life after a catastrophic seven days that have shaken the country to its core.

After a week that began with the country’s largest anti-government protests ever seen and ended with its revered former leader, Luiz Inácio Lula da Silva, blocked from taking up a cabinet post as a result of his alleged involvement in the Petrobras corruption scandal, Rousseff now faces impeachment in Congress that could see her forced out of office next month.

In a move designed to accelerate the hearings against the president, federal deputies sacrificed their usual Friday day off to begin debating Rousseff’s fate. From now on, extraordinary sessions will be held every Monday and Friday in an attempt to force a vote on impeachment by mid-April.

Lucas de Aragão, a partner at Arko Advice, a political risk consultancy, said the deputies’ decision would be influenced by what was happening on the streets. “Many of these parties are non-ideological,” he said. “These guys have no shame in changing sides; they don’t have an ideology to pursue.”

Arko Advice puts the possibility of impeachment at 60%. “It is the most likely scenario, but the game is still being played,” he said.

Foreign investors are betting against her. Brazil’s currency, the real, which fell almost 50% against the dollar last year as the economy shrank by 3.8%, started to surge last week as Rousseff’s demise appeared more probable. On Thursday, the stock market posted its best performance since 2009.

But after one of the most extraordinary seven days in Brazilian politics, predicting developments over the next few hours, let alone weeks or months, is a fool’s errand.

While Rousseff’s approval ratings are barely above 10%, the protests against her government continue to be dominated by Brazil’s white, upper middle-class elite, many of whom are equally as outraged by her leftwing government’s economic policies as by allegations of corruption.

Interestingly, however, few opposition politicians were welcomed at the protests, with many, including Aécio Neves, the losing presidential candidate in 2014, being booed and hounded out of the demonstrations.

If there was any hero for the protesters, it was Sérgio Moro, the investigative judge leading Operation Car Wash, a two-year probe into corruption at Petrobras, the state-run oil firm that was once the largest company in Latin America.

Over the course of the investigation, prosecutors have discovered a massive web of corruption in which the executives of Brazil’s top engineering and construction companies colluded with politicians to overcharge on public works contracts at the oil giant. Dozens of the country’s top businessmen have been sentenced to lengthy prison terms and almost 50 serving politicians are under investigation.

But while many Brazilians initially welcomed Moro’s fearless work, there is increasing unease at both the methods and targets of his inquiry. Much of the investigation has been driven by plea bargaining, in which executives and politicians facing serious jail time have implicated others in the hope of a reduced sentence. Much of this testimony has then been leaked to Brazil’s press, which is overwhelmingly hostile to the ruling Workers’ party.

In the latest phase of the operation, prosecutors targeted former president Lula, still a towering figure in Brazilian politics, who hopes to run for the nation’s top office again in 2018. Lula is accused of being the real owner of two upmarket properties that have been refurbished by some of the construction companies linked to the Petrobras scandal. He denies the charges.

On 4 March, police raided his house and detained the former president for four hours of “coercive questioning”. News of the detention was leaked in advance to TV Globo, Brazil’s dominant television network, which broadcast rolling coverage of the event.

After his release, a clearly emotional Lula described his ordeal as a “kidnapping” and questioned why such aggressive tactics were considered necessary when he had freely presented himself to the police on previous occasions. His supporters reacted with outrage, with the leader of the PT in congress, José Guimarães, promising “war”.

As Rousseff’s government continued to flail last week, with the economy set for another year of 3.5% contraction and a hostile Congress refusing to pass legislation, rumours surfaced that Lula might be appointed to the cabinet, which would both strengthen Rousseff’s government and shield Lula from prosecution. In Brazil, cabinet ministers can only be tried in the “privileged forum” of the supreme court, which can take much longer to get around to hearing cases than lower-level criminal courts.

When news of Lula’s appointment as Rousseff’s chief of staff was confirmed on Wednesday, opposition activists organised immediate protests and vowed to call a general strike.

At this point Moro decided to pour fuel on the fire by releasing some 50 tapes, secretly recorded by police investigators, of Lula talking unguardedly to a wide variety of political allies. One, in particular, proved explosive. The same day as his appointment was announced, Rousseff called Lula to tell him that she was sending him his ministerial papers “in case of necessity”.

The media and the opposition jumped on this ambiguous phrase as proof that the two were colluding to ensure Lula avoided prosecution, sparking further unrest on Wednesday evening and clashes outside the presidential palace where Lula was sworn in on Thursday.

No sooner had the ceremony finished than a court injunction blocked his appointment. After two days of uncertainty, on Friday night a supreme court minister, Gilmar Mendes, upheld the injunction. The government will appeal, but it will have to wait until 30 March.

Meanwhile, around 275,000 government supporters, including trade unions and leftwing movements, took to the streets on Friday night in a major show of force for Rousseff and Lula. Though the numbers were considerably smaller than the anti-government protests the Sunday before, many of them vowed that they would not accept Rousseff’s impeachment.

Max Marcel, 32, a teacher from Ceilândia, a working-class district on the outskirts of Brasília, echoed the sentiments of many. “We are not going to allow a coup,” he said. “The people who want impeachment are those sections of the Brazilian elite who were not able to win at the urns and now want to carry out a judicial and media coup.”

HOW OPERATION CAR WASH UNCOVERED A WEB OF CORRUPTION

17 March 2014 In the first phase, Operation Car Wash, 24 people are arrested accused of money laundering, tax evasions and other crimes. The investigation is named after a network of service stations used as a front to launder bribes.

20 March 2014 Police arrest an executive of energy giant Petrobras, suspected of involvement in money laundering.

26 October 2014 Dilma Rousseff is re-elected as president.

14 November 2014 Another senior Petrobras director is arrested.

15 March 2015 Two million demonstrate against the Rousseff government.

15 April 2015 Police arrest João Vaccari Neto, the former PT treasurer.

19 June 2015 The presidents of construction giants Odebrecht and Andrade Gutierrez are arrested.

3 August 2015 Police arrest José Dirceu, former chief of staff to Lula da Silva.

22 February Police arrest João Santana, the PT’s election guru, who helped Lula and Rousseff to power.

3 March Official statistics show GDP shrank by 3.8% in 2015.

4 March Lula’s properties are raided, and the former president is taken in for “coercive questioning”.

13 March 3.6 million people take part in anti-government protests.

17 March Lula is sworn in as a government minister.

18 March Supreme court blocks Lula’s appointment.