RIO DE JANEIRO — Beleaguered by declining poll numbers, a sputtering economy and judicial investigations, President Jair Bolsonaro convened large protests across the country on Tuesday, Brazil’s Independence Day, which critics fear could be a prelude to a power grab.
In recent days, the president has cast this moment as a do-or-die turning point for his political movement, asking the sizable minority of the electorate that supports him to take to the streets.
“I have three alternatives in the future: being arrested, getting killed or victory,” Mr. Bolsonaro told supporters last week, referring to next year’s presidential elections, which polls show he would lose in a landslide if the vote were held today. “You can be sure the first option, imprisonment, will not happen.”
Many in Brazil see in Mr. Bolsonaro’s actions a parallel to President Donald Trump’s in advance of the 2020 elections, and worry how Brazil, a country with weaker institutions, would weather a similar challenge to electoral institutions or an attack like the Jan. 6 riot in the capital.
A group of more than 150 heads of state, ministers and lawmakers from 26 nations issued a statement on Monday expressing concern that the rallies in Brazil had the potential to turn into an “insurrection” that could undermine democratic norms in the largest nation in Latin America.
“We are gravely concerned about the imminent threat to Brazil’s democratic institutions,” the statement said.
Mr. Bolsonaro has sought to portray Supreme Court justices and other powerful critics as underhanded villains who are setting the stage for the return of his political archrival, the leftist former President Luiz Inácio Lula da Silva, who has surged in the polls after the annulment of graft convictions and the restoration of his political rights.
In recent days, some of the president’s fiery supporters have called for the dissolution of the Supreme Court. Critics of Mr. Bolsonaro fear such rhetoric could lead to political violence, including attacks on the court in Brasília.
The president’s base of supporters includes many members of the military police, a force that is nominally supposed to steer clear of politics. But a recent poll showed that three out of every 10 members of the force intended to take to the streets on Tuesday to support the president.
Mr. Bolsonaro has also called on supporters to take advantage of gun ownership regulations he has loosened to protect themselves in the coming months.
He has led one of the world’s most chaotic responses to the coronavirus pandemic, which has killed more than 584,000 people in Brazil. Unemployment, hunger, inflation, interest rates and inequality have all increased on his watch. Making things worse, an intense drought has reduced water levels at hydroelectric stations, which has the country teetering on the brink of power outages.
The Supreme Court has opened several investigations that have eroded the public’s confidence in Mr. Bolsonaro and his government. They include inquiries into a vaccine procurement corruption scandal and the president’s quest to discredit Brazil’s voting system.
This constellation of challenges has turned much of the electorate against Mr. Bolsonaro, who has railed against polls showing he would lose next year’s presidential election by a large margin to several possible rivals. The president’s attacks on institutions and the voting system could lead to a democratic rupture or a period of deeper instability, opposition leaders say.
“The country is going through its worst moment since the dictatorship,” the governor of São Paulo, João Doria, a presidential hopeful, said Monday. “There can’t be room for flirtation with authoritarianism.”
The president’s surrogates said Tuesday’s rallies would be a peaceful show of the popular will.
“This is a party of democracy!” Damares Alves, the minister of human rights, family and women said in a post on Instagram, in which she was beaming while greeting protesters who began congregating in Brasília on Monday. “Good people, peaceful people are arriving.”
On Monday night, protesters overpowered a police barrier near government ministries. Mr. Bolsonaro was scheduled to address supporters in the capital and later in São Paulo.
Alessandro Molon, an opposition leader in Congress, said he worries that the president, by encouraging large and volatile demonstrations, is seeking to showcase the kind of grass roots support he would have in the event he were to challenge an electoral defeat or disregard the authority of critics in Congress and the judiciary.
“His base is languishing, but it is made up by an increasingly radicalized group, which he intends to use to falsely present as a mandate from the majority of the people,” Mr. Molon said.
Marcelo Neri, an economist and professor at Fundação Getulio Vargas, said Tuesday’s demonstrations are certain to tarnish Brazil’s image abroad and give prospective investors pause, hampering Brazil’s economic recovery.
“There is no reason to add more instability, with events such as tomorrow’s demonstration,” he said.