President Dilma Rousseff’s hopes of seeing out her term of office have received a potentially fatal blow after the biggest party in the Brazilian congress voted to abandon her ruling coalition.

The vote by the Brazilian Democratic Movement party (or PMDB) could trigger a defection from Rousseff’s coalition by other smaller parties, and greatly increase the prospect that she will lose an impeachment vote in the lower house next month and be suspended from office.

To cries of “Workers party out!” and “Onward Brazil!”, PMDB leaders announced their decision to break up the coalition.

“We’re going to try to change the country. The economic and social crisis is very serious,” senator Romero Juca, the PMDB’s first vice-president, told a party meeting in the capital Brasilia.

Rousseff now leads a fragile minority government. Senior officials in the governing Workers party insist the president can still be saved from what they say is a coup attempt against an elected leader who still has more than half of her four-year mandate to serve.

Their hopes depend on securing support from individual members of the PMDB, which is a far from united party. Three PMDB ministers have indicated they may defy orders to quit the cabinet by 12 April.

But government efforts to shore up support look increasingly desperate after the PMDB – which has 68 of the 513 seats in the lower house – decided to leave an alliance that has propped up the government for more than 13 years.

David Fleischer, political science professor at the University of Brasília, said the defection would create a domino effect that is likely to topple Rousseff.

“This is her D-Day,” he said. “[Now the PMDB has left] the possibility of her impeachment increases to 90%.”

The president’s opponents will now have an increased majority on the impeachment committee which could give the go-ahead for a full congressional vote, most likely on 17 April, Fleischer said.

The departure of the PMDB marks a new low in a protracted political crisis triggered by efforts to unseat Rousseff following the Operation Lava Jato (Car Wash) revelations of money laundering, price fixing and bribery at the state-run oil company, Petrobras.

Rousseff’s enemies are attempting to launch impeachment proceedings on several grounds, including ongoing investigations into alleged budget irregularities and campaign finance violations.

The president has insisted there is no legal basis for impeachment, telling reporters last week that any attempt to remove her from power without legal justification would represent a “coup”.

The political trench warfare has paralysed decision making in Brasília, worsening an economy that is deep in recession and heightening public anger. More than a million protesters took to the streets earlier this month in a huge anti-government demonstration.

If 342 of the 513 deputies approve, the impeachment process would move to the senate and Rousseff would be suspended for 180 days while Brazil’s vice-president, Michel Temer – leader of the PMDB – would become interim head of state. A final decision on whether to formally remove her from office would then be taken sometime around October.

(The Guardian)