BRASÍLIA — Brazil’s Senate on Tuesday debated before voting on whether to send suspended president Dilma Rousseff to an impeachment trial, bringing the Olympic host country’s political crisis to a climax.

At the start of the marathon session, Supreme Court President Ricardo Lewandowski reminded senators that they were about to "exercise one of the most serious tasks under the constitution."

Rousseff, a one-time Marxist guerrilla, has likened the impeachment drive to a coup d’etat. Rousseff’s opponents only need a simple majority of the 81 senators’ votes.

They look set to clear the threshold easily, although the debate is expected to stretch into the early hours of Wednesday.

"What we are talking about today is defending the constitution and democracy itself. Those who commit crimes must be held responsible for them," said Senator Aecio Neves, one of Rousseff’s lead rivals.

"The conditions are firmly in place for removing Dilma Rousseff."

About 250 of Rousseff’s supporters demonstrated in central Sao Paulo while in the Senate chamber in Brasilia her allies defended her.

"Today is not a good day for our democracy," said one, Senator Paulo Rocha. Against her, he said, "there is a political alliance that smells of a coup."

 Impeachment vote looms 

It is the final vote before the one that will decide Rousseff’s ultimate political fate, when a two-thirds majority would be needed to strip her of her power and end 13 years of leftist rule in Brazil.

That vote is expected to take place around the end of August, just days after the Rio Olympics end.

The Senate suspended Rousseff, Brazil’s first woman president, on May 12 over accusations of illegal accounting practices and fiddling the budget to mask a slumping economy.

The timing could hardly be more awkward for Brazil, which was meant to be showcasing its burgeoning economic clout and political stability with South America’s first Olympics.

Instead, unpopular interim president Michel Temer -- formerly the vice president -- is fighting to drag the country out of its worst recession in decades as the Senate debates what to do with his former boss and bitter enemy.

Rousseff’s allies in the Workers’ Party point out that many of the lawmakers accusing her are implicated in corruption cases arguably far more

serious than accounting tricks.

But her enemies say her fate is already sealed.

"The president is ever more isolated, a very pronounced isolation that has only gotten worse in recent weeks and now even includes her own party," said

Senator Aloysio Nunes of the opposition party PSDB.

"I have no doubt that the vote will be in favour of impeachment, as it will be at the final trial," he said ahead of the Senate session.

The impeachment trial is set to open around August 25 -- four days after the Olympics closing ceremony -- and last five days, concluding with a judgment vote.—AFP