Brazil’s impeachment duel has tilted back in favour of President Dilma Rousseff after her most strident opponent suffered twin blows from the police and a congressional ethics committee.

Two weeks after the lower house speaker, Eduardo Cunha, launched proceedings to remove the head of state from office, his home was raided by detectives as part of the Lava Jato (Car Wash) investigation into alleged corruption at Petrobras and other major companies.

Hours later the lower house ethics committee announced it would investigate claims that the once-untouchable politician lied about Swiss bank accounts. If proven this could result in his removal from office.

The speaker is now fighting for political survival in the face of calls for his resignation and multiple investigations for taking bribes, including a recent accusation that he received 45m reais (US$12m) from investment bank Grupo BTG Pactual.

The house ethics committee voted 11-9 to begin hearings on whether to strip Cunha of his seat and his political rights for allegedly lying to a congressional hearing on corruption in March, when he said he had no bank accounts abroad.

Cunha triggered impeachment proceedings against Rousseff on 2 December over opposition allegations that she violated budget laws to increase spending during her 2014 re-election campaign.

The ethics case and the police raid may weaken Cunha’s effort to unseat the president and undermine his credibility in the divided Brazilian Democratic Movement party. The PMDB is the largest party in Rousseff’s governing coalition, and its moderate members hold crucial swing votes to decide on her impeachment.

Several of its members were also the focus of Tuesday’s police raids: a federal police statement said the swoop on Cunha’s homes in Brasilia and Rio de Janeiro were among 53 raids carried out in seven states. They included the residences of three prominent PMDB members: the tourism minister Henrique Eduardo Alves, former mining and energy minister Edison Lobão and lower house legislator Anibal Gomes.

But the greatest attention is on Cunha, who is third in the line of presidential succession. He allegedly received a US$5m kickback in the graft scheme uncovered at Petroleo Brasileiro SA, as Petrobras is formally known.

Alerted by Brazilian authorities, Swiss prosecutors located accounts held by Cunha and his wife at the Julius Baer bank and found details of lavish credit card spending.

Ethics committee members almost came to blows on Thursday in a heated argument over attempts by Cunha’s supporters to put off a vote against him.

“Any speaker in the same situation, anywhere in the world, would have already quit his post,” said congressman Chico Alencar, from the leftist PSOL party.

Many Brazilians are less upset about Rousseff’s alleged budget violations than about the worst recession in 25 years and the graft scandal that has ensnared many of her allies.

Though the Workers’ party leader has not been charged in the Petrobras scandal, many question how she could not have known about the corruption, as she was chair of the company from 2003-2010.

Analysts said that she could benefit in her impeachment fight – over separate claims of fiscal wrongdoing – from the extra pressure on Cunha.

“Cunha has effectively been boycotting her in congress. The way that Cunha has led the house has affected the power balance, using his position in the wrong way,” said Antonio Augusto de Queiroz, political analyst at DIAP, an organisation that assesses congress on behalf of the trade union movement. “In the first instance it would be good for the president if he is removed from his position.”

Aninho Mucundramo Irachande, political scientist at the University of Brasilia, said Cunha could not be written off yet.

“He continues to have significant control in the lower house, even though he doesn’t have a say in the ethics council,” he said. “He still has tricks up his sleeve.”

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