RIO DE JANEIRO — Tens of thousands of protesters returned to the streets of cities across Brazil on Sunday to express their ire against President Dilma Rousseff, reflecting a low ebb for her as she grapples with a colossal bribery scandal and a declining economy.

Still, the protests in some cities seemed to lack some of the urgency of huge demonstrations this year calling for the ouster of Ms. Rousseff, a leftist who won re-election just 10 months ago, suggesting tension may be easing somewhat on the president as congressional and business leaders try to prevent a political crisis from intensifying.

The protest in Rio de Janeiro had something of a Carnivalesque feel to it; some demonstrators wore bathing suits as they marched through the Copacabana district as trucks blared samba. But vitriol also marked the event, with some urging the president to kill herself or calling on the military to take power.

“A military intervention may be illegal, but the people have to mobilize to make it legal,” said Rosangela Almeida, 53, an accountant, arguing that action must be taken to prevent Brazil from suffering the economic disarray of neighboring Venezuela. Decades of dictatorship in Brazil left a legacy of hyperinflation and human rights abuses, and political analysts consider the chances of the armed forces returning to power through a coup to be negligible. Still, rising polarization is feeding fears that political infighting could prolong an economic slump.