Eduardo Cunha, president of the Brazilian Chamber of Deputies, participates in a session of the chamber in Brasilia on May 5. (Ueslei Marcelino/Reuters)

An evangelical Christian who plays rock drums and has been likened to Frank Underwood, the ambitious schemer in the Netflix series “House of Cards,” has upended Brazil’s politics since being elected speaker of the country’s lower house four months ago.

Eduardo Cunha hasn’t merely hobbled President Dilma Rous­seff’s coalition government, in which his Brazilian Democratic Movement Party is supposedly her most important ally. His actions have threatened to derail the coalition just months into her second term, leading to a string of revolts that have opened wide fissures in the fragile alliances.

Votes this week on political reform measures show how Cunha operates. A congressional commission worked for more than three months on proposals that were thrown out after Cunha ­invited certain party leaders to lunch at his house and a decision was made thereafter to go straight to a full plenary vote.

This month, Cunha suddenly authorized a vote on a long­stagnant measure to raise the retirement age for Supreme Court and other high-level judges from 70 to 75, ahead of more urgent spending cuts. Approval of the “Walking Stick Amendment,” as it is known, will cost Rousseff five Supreme Court appointments.

José Álvaro Moisés, a political scientist at the University of Sao Paulo, described it as a watershed moment.

“The opposition is not fulfilling its role well. So this space is being occupied by the PMDB,” said Moisés, using the party’s Portuguese abbreviation.

The PMDB also controls Brazil’s Senate under Renan Calheiros and has governed with Rousseff’s center-left Workers’ Party since 2003. But now it plans to challenge the Workers’ Party in the 2018 presidential election, as the aggressive new Congress it controls is changing the balance of power in Brazil. “The legislature also wants to define the agenda of the country,” Moisés said.

“The Brazilian Congress has always been a very docile Congress if you compare it with the American Congress,” said José Mendonça Filho, leader of the opposition Democrats party in the Chamber of Deputies. “Today it has more weight, much more strength.”

Critics have called Cunha dangerous, portraying him as a ruthless and resilient political operator who runs the Chamber of Deputies in an imperial fashion. “He has this sinister side,” said Sylvio Costa, founder of Congress in Focus, a legislative watchdog.

Cunha was dismissive of the Workers’ Party, which ran a rival candidate against him as speaker. “The Workers’ Party cycle is in decline,” he said in an interview.

The PMDB — which some say has long run Brazil behind the scenes — now plans to run its first presidential candidate since 1994. Rousseff’s vice president, Michel Temer, is a potential candidate. So is Cunha, although he said he preferred Rio de Janeiro Mayor Eduar­do Paes.

Rousseff’s popularity is at rock bottom — so low that she has avoided appearing on television recently for fear of setting off the saucepan-banging protests that erupted the last time she made such an appearance. Brazil’s economy is facing recession, inflation is over 8 percent, and Congress has reduced the spending cuts that are part of a fiscal adjustment that Finance Minister Joaquim Levy says Brazil needs to maintain its investment rating.

The country’s economic problems are compounded by a vast corruption scandal in which $2 billion was skimmed off contracts from the state-controlled oil company Petrobras. A former Workers’ Party treasurer, João Vaccari Neto, is among dozens charged in connection with the scheme.

Leading PMDB figures are among politicians who investigators say benefited from the scheme through bribes paid to them and their parties. They include Senate President Calheiros; Edison Lobão, a former party minister of mines and energy; and Cunha.

The party denies the accusations. “The PMDB never received money from Petrobras contracts,” a spokesman said in an e-mail.

In his 2010 election campaign, Cunha received donations from Camargo Corrêa, one of Brazil’s biggest private conglomerates. His party also received donations from Corrêa and Brazilian construction companies linked to the scandal that are on a Petrobras blacklist for future contracts.

Cunha has also denied investigators’ claims that his congressional computer password was used to request that an official commission look into contracts between Petrobras and suppliers — allegedly because bribe money paid via a middleman had dried up. “The attorney general of the republic chose me to investigate — for political interests, in my opinion,” he said. “And the data that he puts there is perfectly refutable.”

‘Ideology of power’

Born in 1958 and married to former television newsreader Claudia Cruz, Cunha has four children. In Rio, he has the support of Domingos Brazão, a counselor at the State Court of Accounts and a former PMDB state deputy who has defended himself against allegations of links to criminal gangs, called militias, whose members include current and former police officers.

Brazão has admitted killing a man but was absolved because the incident was self-defense, he said. In 2012, Cunha and Brazão were both fined by an electoral court for vote-buying in the 2006 elections, when selected Rio condominiums received reductions in their water bills for supporting their campaigns, the court said.

During the military dictatorship that ended in 1985, the PMDB was Brazil’s only legal opposition party, operating as a confederation of all opposing political persuasions, said Rodrigo Motta, professor of history at the Federal University of Minas Gerais, who wrote a book on the party.

“It has no ideology at all. Its ideology is the ideology of power,” Motta said.

And its power lies in strong regional networks.

“It is a party of various regional federations,” said Cunha.

Taking on the Workers’ Party in 2018 could mean fighting Rousseff’s predecessor and political mentor, Luiz Inácio Lula da Silva, because electoral rules would not allow Rousseff to run for a consecutive third term. Wellington Moreira Franco, a former PMDB senator and aviation minister who heads the new undertaking, said the party will fight on an economic platform.

“The right of the left and the left of right participate in, compose the PMDB . . . a party of the center,” Franco said.

Cunha has hit a vein of conservative thinking in Brazil with such crowd-pleasing positions as reducing the age of criminal responsibility to 16 and advocating a “day of heterosexual pride.”

“He is fulfilling the role of the house, which is to represent the people,” said Pablo Rezende, president of the PMDB youth wing.

That could bode well for the party in 2018, even against the perennially popular Lula. “It has the chance to win,” said Paulo Baía, a political scientist at the Federal University of Rio de Janeiro.

On Tuesday, the Chamber of Deputies rejected one of the political reform measures backed by Cunha that would have protected the campaign financing of politicians and parties by companies — a hot topic in Brazil following the recent Petrobras controversy.

The next day, Cunha included in another vote solely the company financing of parties. This time he won. Lawmakers were incensed.

“Eduardo Cunha lost the game, but is the owner of the ball. So he said, ‘I didn’t like the result; let’s play again,’ ” Júlio Delgado, a deputy in the Brazilian Socialist Party, told the Folha de S.Paulo newspaper.

Brazilian politics is a rough-and-tumble game. Increasingly, it appears, Eduardo Cunha does not mind playing dirty to win it.

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