BRASÍLIA — After months of tirades, secret maneuvering and legal appeals, Brazil’s Senate began debating on Wednesday whether to impeach President Dilma Rousseff, suspend her from office and put her on trial.

The debate, followed by a vote as late as Thursday morning, is a watershed in the power struggle consuming Brazil, a country that experienced a rare stretch of stability over the last two decades as it strengthened its economy and achieved greater prominence on the world stage.

Now, those gains are unraveling. Brazil is facing its worst economic crisis in decades, huge corruption cases across the political spectrum and a bitter feud among its scandal-plagued leaders — just months before the world heads to Rio de Janeiro for the Summer Olympics.

Ms. Rousseff, who is accused of manipulating the budget to hide the depths of Brazil’s economic woes and bolster her own re-election prospects, is widely expected to be ousted by the Senate, ending 13 years of political dominance by her leftist Workers’ Party.