RIO DE JANEIRO — The Rio Olympics just ended, and Brazilians are quickly switching their attention to another heated competition consuming the country: the bare-knuckle brawl for the presidency.

On Thursday, the Senate began its impeachment trial of Dilma Rousseff, the president who was suspended in May to face charges of manipulating the federal budget in an attempt to conceal the country’s economic problems.

She is widely expected to lose, and senators could vote as early as next week. Her opponents need two-thirds of the 81-member Senate, or 54 votes, to convict her. If they succeed, Michel Temer, the interim president and former vice president, will be president until the end of the current term in 2018.

The impeachment trial could serve as the bookend for one of the most tumultuous periods in Brazil’s democracy, which was re-established in 1985 after a long military dictatorship. Mr. Temer’s scandal-plagued centrist Brazilian Democratic Movement Party is taking control of the government, supplanting Ms. Rousseff’s leftist Workers’ Party, which is also engulfed by corruption scandals.