Brazil is bracing for a fresh bout of political turmoil after the president, Michel Temer, became the country’s first sitting head of state to be formally charged with a crime.

Less than a year after taking power, the deeply unpopular leader was formally accused of corruption by the attorney general Rodrigo Janot on Monday night and could now face a lower house vote on whether he should be tried by the supreme court for taking bribes.

In a damning indictment to the supreme court, Janot alleged Temer took millions of dollars in bribes from meat-packing giant JBS. The attorney general said the president had “fooled Brazilian citizens” and compromised the image of the country.

Temer said on Tuesday that he was the victim of a political defamation campaign. “I have been denounced for passive corruption without having received anything of value. Where is the concrete proof that I received something of value?” he said in a statement made before journalists in the Planalto Palace.

As he has done repeatedly, the president turned on his accusers, insisting Janot and his supporters were damaging the national interest. “They want to paralyze the country, they want to paralyze the government,” he said. “I will not run away from the battles, nor the war that lies before us.”

The ruling coalition currently has sufficient votes to defend the president in Congress, where a two-thirds majority would have to approve a trial. But the looming battle will further undermine the credibility of Temer, whose approval ratings have slumped to 7%.

His predecessor Dilma Rousseff – who was ousted in an impeachment plot in May 2016 – was quick to note that her former running mate was now accused of greater crimes than those for which she was removed from office last year.

“The result of the 2016 coup: leaving the country in the hands of the only president indicted for corruption,” she tweeted.

Janot launched an investigation last month into Temer for bribery, obstruction of justice and activity in a criminal organization.

These allegations followed the release of a secret recording of a late-night conversation earlier this year between Temer and the JBS executive Joesley Batista, in which the president appeared to endorse hush money payoffs to former house speaker Eduardo Cunha, a member of Temer’s party who is serving a 15-year sentence for corruption. Police have since confirmed the authenticity of the recording and said there is sufficient evidence to indict the president.

“The circumstances of this meeting [with Batista] – at night and without any register in the official schedule of the president of the Republic – reveal the intent not to leave traces of the criminal actions already taken,” Janot claimed.

Temer has resisted pressure to stand down and tried to demonstrate leadership last week by making an official visit to Norway and Russia. But his attempt to shift the focus backfired when Norway’s prime minister, Erna Solberg, publicly lectured him on the need for Brazil to deal with its corruption woes.

Norway also halved its contribution to an Amazon rainforest fund due to the Brazilian government’s failure to address accelerating deforestation.

Analysts say Temer’s position is weakening as major news outlets turn against him and some allies – such as former president Fernando Henrique Cardoso – call on him to resign.

“Temer has never been so fragile,” said Lúcio Flávio Rodrigues de Almeida, a politics professor at the Pontifical Catholic University of São Paulo. “His support levels are at a low and continue to fall. There is also a strike under way. This make make him suffer pressure even from his allies. He is on a tightrope.”

However, the president still has the backing of the leader of the lower house, Rodrigo Maia, who could block the judicial process. The main business group, the National Confederation of Industries, also continues to endorse him in the hope that he will push through pension and labour reforms which will help companies.

Temer – a constitutional scholar – has changed justice minister twice this year in an attempt to strengthen his hand when dealing with judges, prosecutors and police, but time could wear him and his congressional majority down, particularly if Janot files other accusations.

“This crisis will not be solved today or even this week. There is a big change of this dragging out for a long time and perhaps only coming to a conclusion towards the end of the year,” said Rogério Arantes, a political scientist at the University of São Paulo. “Temer has the capacity to resist, due to his base in Congress, which needs to authorise the accusations against the president. This fact might help him in the next days and weeks, but in the next months, it’s impossible to say.”

His fate is likely to depend on whether ruling party legislators consider him a liability ahead of next year’s presidential election or whether they feel he can push through unpopular reforms.

“The proximity to the voters at this point could be an important factor in determining whether his allies will continue their support,” said Mara Telles, a professor at Federal University of Minas Gerais.

Additional reporting by Shanna Hanbury