Updated at 8:20 A.M. E.D.T.

Luiz Inácio da Silva, after winning a runoff election by a narrow margin, will on January 1 return to the Alvorada Palace for a third term of the presidency of Brazil, though this time facing political hurdles that could spell trouble ahead.

In a nail-biting election, Mr. da Silva won 50.9 percent of the vote, against President Bolsonaro’s 49.1 percent. It was the tightest election in the last three decades, and the right is far from vanquished. Mr. da Silva will have to deal with a Congress dominated by conservatives, and officials who govern Brazil’s top states are also on the right.

This means that Mr. da Silva could face street violence in the wake of an exceptionally close vote that was stoked by high-octane rhetoric on both sides in the final stages of the campaign. In the longer run he will have to contend with a hostile Congress that could hamper his ability to govern effectively.

This has been the most polarizing presidential election since the establishment of the Sixth Republic and restoration of democratic government in a process that began in 1985, saw the adoption of a new constitution in 1988, and was capped by the full constitution coming into full force in 1990. The election just held was marked by political violence that has spread throughout the country.

In the wake of the voting Sunday, the incumbent president, Jair Bolsonaro, has failed to make a public appearance or concede defeat. He had previously warned that he might not accept the election results, provoking concern that he might take a page from President Trump’s playbook and try to challenge the vote count. 

According to a professor of international relations at the Federal University of Sao Paulo, Regiane Nitsch Bressan, Brazilians fear that any denial of the vote by Mr. Bolsonaro could trigger new protests in the street. Some of Mr. Bolsonaro’s supporters are “violent people who have been goaded by his violent speech,” Ms. Nitsch Bressan says. 

Mr. Da Silva, though, is no stranger to divisive rhetoric, suggesting during the campaign that Brazilians who vote against him are “enemies,” Tobias Kaufer of Deutsche Welle reports.

At the moment, though, the expectation is that on January 1, the 77-year-old leader of the Workers Party will return to the Alvorada presidential palace. Mr. Da Silva has vowed to bring back what he describes as the “economic success” from his last time in office, when, he has claimed, between 2003 and 2010, 28 million people were lifted out of poverty. 

Yet Mr. Kaufer observes that Mr. Da Silva’s strident campaign attacks during the campaign were “designed to distract Brazilians from his own failings, and those of his party.” He notes that following the rule of Mr. Da Silva’s party, “Brazil found itself in such a bad state that voters turned to Bolsonaro in 2018,” and that this “victory was not the result of fake news, as is so commonly claimed by populists.” 

Mr. Kaufer also notes that “never in Brazil’s history has there been greater destruction of rainforest than under Lula.” He contends that while Mr. Bolsonaro has come under fire for “trivializing Brazil’s former military dictatorship,” Mr. Da Silva  has endorsed “brutally oppressive left-wing regimes of Cuba, Venezuela and Nicaragua, from which people flee constantly, some of them dying as they make their escape.”

Though Mr. da Silva has yet to present a detailed economic plan, during his victory speech on Sunday he said that he would  “rebuild the country,” and fight against poverty and hunger in Brazil. 

This sets the stage for a reprise of Mr. Da Silva’s tenure, during which whatever gains were made against poverty came at the cost of expensive social programs that could do more harm than good in the long run.

In an interview with the Economist before the election, Mr. Da Silva sought to refute accusations by Mr. Bolsanaro that he is a “devil who wants to impose communism on Brazil.”

Mr. Da Silva pointed to the 4.5 percent average annual growth of Brazil’s economy during his tenure, the fall in the national debt to 40 percent from 60 percent of the gross domestic product, and the reduction in the rate of inflation, to just under 6 percent from 12 percent. He also hailed an “increase in the minimum wage.”

Yet the Economist warns such gains could prove elusive this time around: “his job will be much harder than it was when he took office in 2003.”

Mr. Da Silva’s challenges will include an uncooperative legislature. As problematic as the protests over Mr. Da Silva’s election might be, the bigger hurdle is likely to come from a Congress that one Argentinian lawyer, Ines Liendo, tells the Sun could prove to be “resistant” to enacting Mr. da Silva’s agenda. 

Since Mr. da Silva left the presidency, Congress has gained more authority. After impeaching a president, Dilma Rousseff, in 2016, it shrunk the president’s public spending power and blocked big parts of Mr. Bolsonaro’s agenda.

“From the economic point of view, Lula will have to take all of the necessary steps to get rid of Congress’s spending limit, or he will not be able to do much of what he promised,” an economist of the University of Sao Paulo, Leda Paulani, told the newspaper La Nacion. 

In the October 2 first round of elections, Mr. Bolsonaro’s Liberal Party gained 99 seats in the Chamber of Deputies — the largest number since 1998. Mr. da Silva’s party has 80, a problem that will force Mr. da Silva to negotiate with Brazil’s center force in Congress, known as the Centrão. The Centrão encompasses several political parties, and has 48 percent — 220 — of the seats in the Chamber of Deputies. 

Ms. Paulani says that internationally, Mr. da Silva will face more obstacles than at the beginning of the decade. With the fraught  relationship between America and Communist China, global inflation, and the impact of the Russian-Ukrainian war, “it’s difficult to imagine a global economic resumption, which interferes with Brazil’s chances of recovery,” Ms. Paulani says.

The governors of Brazil’s most populous states will also present a challenge for Mr. da Silva. A conservative candidate, Tarcísio de Freitas, was elected on Sunday to become the governor of Brazil’s richest state, São Paulo. As Mr. Bolsonaro’s former minister of infrastructure, Mr. Freitas won 55.7 percent of the votes.

In the October 2 first round of elections, Mr. Bolsonaro’s candidates won re-election in the big states of Rio de Janeiro and Minas Gerais. Claudio Castro was re-elected for governor in Rio de Janeiro with 58.6 percent, and Romeu Zema was re-elected in Minas Gerais with 56 percent.

Brazil’s elections were followed closely by the presidents of Latin America, a region in which now the most important economies are all governed by leftist governments. Among them is Argentina’s leftist Alberto Fernandez, who aims to re-establish ties with Brazil, after Mr. Bolsonaro distanced himself from the region. 

“Your victory opens a new era for the history of Latin America,” Mr. Fernandez tweeted after Mr. da Silva’s triumph was announced.