SÃO PAULO—The national mood fluctuates between a festive carnival parade and a bitter family feud as Brazilians tensely await Sunday’s congressional vote on whether to impeach President Dilma Rousseff.

Here in Brazil’s largest city, pro-impeachment activists have pitched tents and draped antigovernment banners on the main commercial drag. Among their props is a gigantic inflatable yellow duck, alluding to a Portuguese expression that roughly translates as, “We won’t pay the tab for what isn’t our fault.”

In Rio de Janeiro on Monday, intellectuals and artists including songsmith Chico Buarque and Leonardo Boff, a social-activist priest, staged a pro-government rally in the bohemian Lapa neighborhood, and signed a manifesto decrying the impeachment push as a threat to democracy.

But the colorful street theater underlines social fissures that have widened over the past decade amid a sagging economy and rising public anger at corruption among Brazil’s economic and political elites.

The showdown between Ms. Rousseff and her congressional adversaries has opened rifts among Facebook friends and family members. Punches have been thrown by angry lawmakers on national television. Bloodier altercations have broken out among red-shirted supporters of Ms. Rousseff’s leftist Workers’ Party and opponents decked out in the yellow-and-green jerseys of the national soccer team.

“All this ends up being bad for democracy itself,” said  Pedro Fassoni Arruda, a political scientist and professor at the Pontifical Catholic University of São Paulo, who like many commentators has compared the atmosphere to a rowdy soccer match.

Brazil’s political temperature is rising ahead of Sunday’s climactic vote, after a special congressional committee voted on Monday to support a recommendation for impeachment. If two-thirds of the full Chamber of Deputies votes on Sunday to support impeachment, Ms. Rousseff’s case will be sent to the Senate for trial.

The charges against Ms. Rousseff stem from accusations that she used accounting tricks to hide a growing federal budget deficit, allegations she denies.

Politicians have set the nasty tone for the nation. Monday’s televised commission hearing showed adversaries shouting each other down with cries of “Dilma, out!” and “There will not be a coup!” Government foes brandished blow-up dolls of Ms. Rousseff’s mentor and presidential predecessor,  Luiz Inácio Lula da Silva, sporting prison pinstripes.

Although Brazil’s social divisions aren’t as acute as those in neighboring Venezuela, the roiling discontent and disillusionment have upset the country’s self-image as a tolerant and congenial society, as ugly incidents of intimidation have multiplied in recent weeks.

In the southern city of Porto Alegre, a pediatrician refused to treat the son of a local official aligned with the Workers’ Party. In São Paulo, a prominent sports columnist, Juca Kfouri, was verbally abused at his home after he took a public stand against impeachment.

Mr. Kfouri, who writes for the Folha de S.Paulo newspaper, said in an interview that he is not a Workers’ Party supporter, but doesn’t think Ms. Rousseff has done anything that would justify impeachment.

“I have never seen such intolerance,” said Mr. Kfouri, who was arrested in 1971 for opposing the military dictatorship that ruled Brazil for two decades before democracy was restored in 1985. “We are no longer able to discuss politics.”

Some believe the silver lining in Brazil’s stormy outlook is that smartphones and social-networking apps have made it easier for ordinary citizens to have a say in the rancorous debate.

Filmmaker Anna Muylaert, who opposes impeachment, said Brazil and other countries are experiencing “a very democratic, historic period” that bodes well for the future.

The country’s greater problem is the corrupt legacy of the past, said Ms. Muylaert whose 2015 feature, “Que Horas Ela Volta?” (“The Second Mother?”) deals with subtle class tensions between an affluent São Paulo family and its devoted housekeeper.

“I think that comes from the way we were colonized 500 years ago, the way the Portuguese came here to get the gold, to use the Indians, and not thinking of building a nation,” she said. “That is a curse that is still going on.”

For now, though, many Brazilians are eagerly looking forward to Sunday’s vote, and not bothering too much about what came before or what comes next.

“If the impeachment is approved, there will be a huge party,” enthused  Cezar Leite, who heads a regional chapter of Vem Pra Rua (Come to the Street), an anti-Rousseff group, in the city of Salvador in the northeast state of Bahia.

“Salvador will wake up in a carnival,” Mr. Leite said.