Mr. Lula, 80, had framed his candidacy as a vote for democracy and the only way to bar the return of the Bolsonaro family to power. He has frequently and defiantly clashed with Mr. Trump, who attempted to use tariffs and sanctions to keep Mr. Bolsonaro’s father, Jair, out of prison.

Mr. Lula’s victory snapped a string of seven straight wins by right-wing leaders in the region over the last 18 months, and suggested that Latin America’s left-wing forces still wield some influence despite the losses.

Looming over the contest was an epic political struggle that has roiled and defined Brazilian politics for more than a decade. Mr. Bolsonaro ran in lieu of his father, who could not stand for office because he was convicted of attempting a coup against Mr. Lula after losing the last election in 2022. He was sentenced to 27 years in prison and is serving his time at home because of health reasons.

The candidates offered starkly different visions on issues that included fighting organized crime and revitalizing a sluggish economy. The outcome could reshape Brazil’s trajectory on many divisive issues for years to come because the next president will have the right to fill four open seats on the country’s powerful Supreme Court, which has 11 seats in total.

Here’s what else to know:

• One town’s story: Nanuque, about 500 miles north of Rio de Janeiro, is a cattle-raising, churchgoing town where crowds turn out on foot for an annual march for Jesus and on horseback for the nation’s independence day. It is a microcosm of Brazil, offering clues to Mr. Lula’s lackluster showing in the first round and Mr. Bolsonaro’s rise. Read more ›

• Right-wing leaders: Over the last 18 months, right-wing candidates had won the last seven presidential elections in Colombia, Chile, Honduras, Bolivia, Peru, Ecuador and Costa Rica. A win by Mr. Bolsonaro would have given Mr. Trump a new ally in his war on drugs. Read more ›

As Brazilians headed to the polls on Sunday, the question looming over Latin America’s largest democracy was whether Mr. Trump would have an influence.

He has not openly championed either Brazilian candidate. But the Trump administration did try in more subtle ways to lift the right-wing challenger, Flávio Bolsonaro, who is running against President Luiz Inácio Lula da Silva, a leftist.

Having watched Mr. Trump wade into other elections and experienced his failed attempt to intervene in the trial of Mr. Bolsonaro’s father, who was ultimately convicted for plotting a coup, Brazil has sought to erect a firewall to try to shield its vote from potential U.S. meddling. (The elder Bolsonaro is currently serving a 27-year sentence at home, given his health.)

The Trump administration has rejected Brazil’s claims that it is seeking to interfere, even though it tried this summer to send a U.S. delegation to investigate Brazil’s electoral integrity.

Mr. Lula’s campaign, which was trying shore up his position before the runoff against Mr. Bolsonaro, filed a complaint with the nation’s electoral court on Oct. 10, demanding fair treatment online.

“The scenario is,” the complaint said, “that of a platform illegally practicing algorithmic selectivity, in the midst of a fierce presidential contest.’’

Meta has firmly rejected claims of political bias, asserting firmly in a response to the court that it “does not operate its systems to harm or favor candidacies.”

But in Brazil, where social media and disinformation have played a central role in recent elections, fears that online debate could again sway a narrow presidential race have touched a nerve.

In Brazil, a nation of 214 million, disinformation has defined elections for nearly a decade. The country has some of the world’s strictest regulations against spreading falsehoods during elections.

But the deluge of A.I. — made by candidates, strategists and ordinary citizens — has become a stark test of the nation’s capacity to police online content, posing a new challenge for the Brazilian authorities trying to protect the integrity of the vote.

“We made the rules, now we’re watching to see what happens,” said Kássio Nunes Marques, chief justice of Brazil’s electoral court, which oversees the vote.

But earlier this year, the justice’s reputation was shattered when he was publicly linked to a banker accused of fraud. According to a leaked police dossier, Justice Moraes had exchanged text messages with the banker, who was seeking help in avoiding arrest and mentioned paying millions to a law firm run by the justice’s wife. The police have never said if Justice Moraes responded to the request or helped the banker in some way.

Still, the revelation has become a major issue in the presidential election being decided on Sunday.

For starters, President Luiz Inácio Lula da Silva, a leftist, was saddled with the fallout of the scandal at the Supreme Court that tarnished Justice Moraes, his ally.

But the scandal has also galvanized many right-leaning voters in their support for Jair Bolsonaro’s son, Flávio, who is challenging Mr. Lula for the presidency. Mr. Bolsonaro used the scandal to whip up support in his stump speeches.

“To vote for Lula is to vote for Alexandre de Moraes,” Mr. Bolsonaro recently told a crowd of supporters. “And I’m not going to let that happen.”

“It gave Flávio’s campaign a simple slogan,” said Luciano da Ros, a Brazilian political scientist. “And it united different segments on the right around a powerful common enemy.”

Mr. Lula, eager to shield his campaign, has tried to distance himself from Justice Moraes. “Nobody is above the law,” he said in an interview. He urged an investigation into the justice’s conduct and a broad judicial overhaul.

Now Mr. Lula, weighed down by widespread perceptions of rising crime and economic woes, faces a challenge from the former president’s son, Flávio Bolsonaro, a right-wing senator. Mr. Bolsonaro’s formidable performance in the first voting round this month gave him the edge going into a two-way contest.

The outcome will have a profound effect on Brazil and its relations with the United States in particular. Here are some of the major issues at stake.

Security

Mr. Bolsonaro has already said he would add Brazil to the Trump administration’s anti-cartel coalition, called the Shield of the Americas, and work with the United States to fight Brazilian gangs.

He suggested in social media posts last year that he would welcome U.S. military intervention in Brazil, though he denied that in recent interviews, saying the cooperation would be limited to intelligence. But it was Mr. Bolsonaro who successfully lobbied Mr. Trump to designate two Brazilian gangs as terrorist groups.

Mr. Lula has resisted joining the coalition, warning that intertwining too closely with the United States on security matters could threaten the nation’s sovereignty.

Trade

The Trump administration imposed tariffs on Brazilian products in an unsuccessful pressure campaign to disrupt the prosecution of Jair Bolsonaro. Many of those tariffs were eventually scaled back, and Brazil’s economy has remained largely unharmed by President Trump’s tariff campaign.

Another term for Mr. Lula, however, would increase the risk of more economic conflicts with the United States that might hurt the Brazilian economy. Of course, Mr. Bolsonaro would not be immune to those problems; Mr. Trump has been known to levy tariffs against allies as well as adversaries.

The Trump administration has signaled an interest in importing Brazilian oil to counter disruptions related to the Iran war and the country’s rare-earth minerals to reduce U.S. dependence on China for those resources. Mr. Bolsonaro is expected to align Brazil more closely with the United States than Mr. Lula has on trade issues, but neither leader can afford to anger China, a major trading partner.

The election could also affect Brazil’s ability to negotiate trade with the United States as a bloc with other countries in the region.

“Brazil’s relations with its neighbors have been extremely challenging,” said Carolina Moehlecke, an assistant professor of international relations at Getúlio Vargas Foundation, a research institution. This was especially true of its neighbor, Argentina, she added, whose right-wing president is a close ally of Mr. Trump. Mr. Bolsonaro, she said, might have an easier time cooperating with fellow right-wing leaders in Latin America.

Domestic Policy

If Mr. Bolsonaro carries the vote, conservationists fear a return to his father’s policies of allowing rapid deforestation in the Amazon rainforest, a trend that was largely reversed under President Lula. The younger Mr. Bolsonaro does not believe that climate change is caused by humans and has defended opening up protected lands to mining and farming.

He has also pledged to stem the nation’s rising debt. If he attempts to accomplish that through cuts to public spending, that could prove politically sensitive, Ms. Moehlecke said, especially when it comes to social welfare policies with broad popularity in Brazil. In the lead-up to Sunday’s elections, Mr. Lula had promised to increase welfare payments.

Democracy

Mr. Lula has framed the election as a test of the nation’s democracy and portrays the Bolsonaros as a threat to democratic institutions. Ms. Moehlecke said it was likely Mr. Bolsonaro would take the country in a more authoritarian direction, though his rhetoric is generally tamer than his father’s.

But if Mr. Bolsonaro wins, his party’s gains in the legislature could allow him to deliver on some of his most polarizing promises: amnesty for his father, pardons for rioters who stormed Brazil’s halls of power after the last election, and a Senate more willing to try to remove justices who convicted his father.

If Mr. Lula wins, he most likely will face significant checks against his power. Right-wing candidates, including four other members of the Bolsonaro family, have made significant strides in the nation’s legislative races.

Voters will decide whether to give President Luiz Inácio Lula da Silva another term or elect Flávio Bolsonaro, a senator and the son of the last president.

Mr. Bolsonaro heads into the race as the front-runner, having won more ballots than Mr. Lula in the first round of voting this month but not enough to avoid a runoff. Still, the margin was the smallest in Brazil’s history and most polls show the two men in essentially a statistical tie.

The two candidates offer starkly different visions for the future of Latin America’s largest democracy on issues that include how to fight organized crime, shake up a sluggish economy and restore trust in Brazil’s institutions.

Who are the candidates?

The presidential contest is a familiar one, pitting Mr. Lula, once again, against a Bolsonaro. This time, though, he will face off against the eldest son of the former President Jair Bolsonaro, whom Mr. Lula defeated in 2022.

Mr. Bolsonaro was convicted last year on charges of orchestrating a vast coup plot, which included plans to assassinate Mr. Lula.

Mr. Lula, 80, has framed his candidacy as a vote for democracy and the only way to bar the return of the Bolsonaro family to power. His argument has struck a chord with Brazilians worried about the health of Brazil’s democracy if another Bolsonaro leads the country.

Mr. Lula has also promised to protect Brazil’s sovereignty, standing up to Mr. Trump last year when he tried, through tariffs and sanctions, to intervene in Jair Bolsonaro’s criminal trial.

Yet Mr. Lula, an enduring presence in Brazilian politics who is now seeking a fourth term, has also struggled to energize many voters hungry for political and economic change. The first round of voting suggested that he has lost touch with many working-class Brazilians who were once his staunchest backers.

Mr. Bolsonaro, 45, seeking to harness the affection many right-wing voters still have for Jair Bolsonaro, has promised to restore his father’s conservative agenda. At the same time, he is trying to appeal to women and independent voters by casting himself as a more moderate successor by avoiding the sexist, racist and homophobic rhetoric that his father often employed.

Mr. Bolsonaro has said that, if elected, he would seek amnesty for his father and rioters jailed for storming Brazil’s halls of power after the last election, in an episode reminiscent of the attack on the U.S. Capitol.

Each candidate has cast the other as corrupt. Mr. Lula has pointed to a corruption investigation into Mr. Bolsonaro over millions of dollars he raised for a biopic about his father from a disgraced banker at the center of a billion-dollar fraud scandal. Mr. Bolsonaro has seized on a past corruption scandal that landed Mr. Lula in jail, a conviction that was later set aside.

What are the big issues?

Brazilian voters are seeking solutions to various challenges, including the spread of criminal networks and persistent economic stagnation that has left many people under financial strain.

Mr. Bolsonaro, seizing on voter worries about crime, has made fighting drug gangs a cornerstone of his campaign. He has vowed to “declare war” on crime groups and build five new maximum-security prisons inspired by the incarceration model adopted by El Salvador’s strongman, Nayib Bukele.

Mr. Lula has championed a different approach that targets the finances and weapons of organized criminal organizations, arguing that these groups must be dismantled from the top. He has pointed to Brazil’s history of bloody police operations that take out foot soldiers but fail to capture gang leaders.

Mr. Bolsonaro, inspired by President Javier Milei of Argentina, has adopted a pair of giant scissors as a symbol of a leaner state and promised $40 billion in cuts to public spending. He has also pledged to lower taxes and reduce red tape for entrepreneurs, seeking to appeal to a growing number of Brazilian workers who have migrated to the gig economy.

Under Mr. Lula’s watch, Brazil’s economy has remained largely unscathed by American tariffs while unemployment rates have dropped to record lows. Still, rising food prices and mounting household debt have weighed on his approval ratings.

Mr. Lula, seeking to reverse his fortunes, recently expanded a debt-relief program under which the government will buy billions in delinquent consumer loans. And just days before the elections, he banned online betting, which has accelerated Brazil’s personal debt crisis.

Has the U.S. interfered?

In Brazil, a nation where protecting its sovereignty runs deep, worries about America putting its thumb on the vote has loomed large.

Mr. Lula, casting Mr. Bolsonaro as a U.S. puppet, has accused the Trump administration of trying to sway the vote in his rival’s favor to seize Brazil’s vast natural resources, including critical minerals.

He has also frequently reminded voters that Mr. Trump applied steep tariffs on Brazil after a brother of Flávio Bolsonaro lobbied the White House as part of a campaign to keep their father out of prison. When those efforts failed, Mr. Trump dropped most of those tariffs.

While Mr. Trump has not formally endorsed the younger Mr. Bolsonaro, he has seemed willing to support him in more subtle ways. This has included designating Brazilian gangs as terrorist organizations, which helped Mr. Bolsonaro cast Mr. Lula as weak on crime.

Following Mr. Bolsonaro’s first-round win, Mr. Trump was quick to celebrate. “It’s a big victory,” he told reporters.

In recent days, questions have also emerged over the impartiality of American social media companies after Mr. Lula and independent watchdog groups accused Meta of giving his right-wing rival favorable treatment on its platforms.

What is the role of social media in the election?

In the race to sway a deeply divided Brazil, social media has emerged as a contentious political battleground since the first round of voting. And Brazil’s electoral court has become the referee that some accuse of picking sides.

The court, led by a justice appointed by Mr. Bolsonaro’s father, has ordered social media posts by news outlets criticizing Flávio Bolsonaro removed and barred Mr. Lula from posting some negative news stories about his rival.

Justice Kássio Nunes Marques, who leads the electoral court, set off widespread outrage by appearing to target a popular channel on WhatsApp, a platform long dominated by Mr. Bolsonaro’s right-wing movement, aimed at mobilizing Mr. Lula’s supporters on social media and on the streets.

The channel, which quickly attracted more 10 million followers, landed in the center of a firestorm when Mr. Bolsonaro asked the electoral court to shut it down, claiming it was spreading fake news.

Ultimately, the channel was allowed to keep operating, though Justice Nunes Marques pressed Meta to dig deeper to see if it was breaking any electoral rules.

When will results be known?

On Sunday, Brazilians will cast their votes using electronic voting machines; experts say it is one of the fastest and most secure electoral systems in the world. Voting in Brazil is compulsory and, in 2022, turnout for the second round of elections was close to 80 percent.

Brazil’s electoral authority will start releasing results after polls close at 4 p.m. E.T., and a final tally will most likely be announced a few hours later. The count can be followed in real time here.

A visit to Nanuque, a cattle-raising, churchgoing town 500 miles north of Rio de Janeiro, where crowds turn out on foot for an annual march for Jesus and on horseback for the nation’s independence day, offers clues to Mr. Lula’s lackluster showing and Mr. Bolsonaro’s rise.

The town of 35,000 sits in the bellwether state of Minas Gerais, which has backed the winner in every presidential election since 1988, when democracy returned to Brazil after a military dictatorship.

In the 2022 race, Nanuque, pronounced nah-NEW-key, was the most closely divided of Brazil’s 5,569 municipalities, with Mr. Bolsonaro’s father, Jair Bolsonaro, winning by one vote. (Jair Bolsonaro lost that election to Mr. Lula and was convicted of plotting a coup after trying to hold onto power.)

In 2026’s first round, the younger Bolsonaro finished ahead by two percentage points, the same margin he claimed in Brazil as a whole.

Mr. Bolsonaro’s ability to win similar towns — rooted in agriculture and with a strong Evangelical Christian presence — contributed to his strong first round showing.

Video

Where Brazil’s Left Is Losing Voters

Far from Rio and São Paulo, small towns like Nanuque, with big agricultural businesses and a surging evangelical Christian movement, are swinging to the right.CreditCredit...Seth Kugel for The New York Times

He won 79 percent of towns with a large agricultural sector, a high percentage of evangelical Christians and fewer than 50,000 residents, according to an analysis by Marco Faganello, a political data scientist at Fundação Getulio Vargas, a Brazilian university. Jair Bolsonaro won 53 percent of such towns in 2022’s first round.

In interviews with scores of voters in Nanuque, including truck drivers, cattle ranchers, farmworkers, business leaders and civil servants, those who have abandoned Mr. Lula cited unfulfilled economic promises, his past corruption scandals and their frustration with health care, among other reasons.

While many on the left remain staunch supporters of Mr. Lula, others who had voted for him before expressed fatigue over an 80-year-old incumbent running for a fourth term. His Workers’ Party has been in power for 18 of the last 24 years.

Valdirene Santos Moura, a cook who has voted for Mr. Lula before, acknowledged his accomplishments, including introducing programs that helped the poor. But now, she said, she was “tired of him already.”

Geremias Alves de Souza, a coffee picker, dropped his voice so his wife would not hear him say he was voting for Mr. Bolsonaro. He said he associates the younger Mr. Bolsonaro with his father’s tough on crime policies.

Other voters said their support for Mr. Bolsonaro was based not on his track record — which they said they were unfamiliar with — but on their affection for Jair Bolsonaro.

Some said they were simply fed up with politics and were planning to abstain on Sunday.

One is Jovenildo Carvalho, 45, who runs a start-up that uses drones to deploy wasps to attack caterpillars that ravage sugar cane fields.

Mr. Carvalho, who grew up with no electricity and wore Che Guevara T-shirts in college, said he has no faith in either candidate’s ability to lead the country, and was frustrated by Brazil’s deeply polarized political landscape.

“I’d like to see Brazil without the veil of fanaticism and blind passion that it has today,” he said.

Big business has big grudges

Agribusiness in Brazil, which includes farming, cattle ranching, meatpacking plants and ethanol distilleries, has become a behemoth, accounting for a quarter of the country’s economy. For the first time, Brazil may soon surpass the United States in agricultural exports.

The sector’s leaders are among Mr. Lula’s biggest detractors, criticizing him over high interest rates, environmental regulations and gas subsidies that have reduced ethanol demand during the Iran war.

“If it were Lula against a stray dog, everyone would vote for the stray dog,” said Luiz Daniel Silva Rocha, whose family owns DASA, a large sugar mill and ethanol distillery outside Nanuque that employs hundreds of people.

The biggest target for local business leaders is Mr. Lula’s signature welfare program, known as Bolsa Família, which provides cash transfers to low income families. Brazilians agree that it has helped pull millions out of extreme poverty, but some now consider it a handout to those who aren’t financially desperate.

“In Brazil today, the policy is to reward those who don’t work,” said Ângelo Márcio Sousa Silva, DASA’s general manager.

Nearly 3,000 families in Nanuque receive cash transfers, according to government data, and business leaders say it has made it hard for them to fill jobs. Between DASA and the town’s largest employer, a meatpacking plant, there are about 120 full-time vacancies, leaving the plants operating below capacity.

The Bolsa Família program came up repeatedly as a driving force behind people’s votes for both candidates, far more than topics that dominate election talk among urban elites, like a scandal roiling Brazil’s Supreme Court or worries about U.S. interference in Latin American elections.

People who work in the informal sector — as day laborers on farms or cleaning houses — but still receive cash benefits remain loyal to Mr. Lula.

Letícia Silva de Almeida, 33, is among those. She works seasonally helping harvest coffee and earns $24 per day. She also receives $150 a month through the cash transfer program, even though she said that money was not essential.

“If they cut it off today, I’d be OK,” she said.

That mind-set infuriates others. Tatiane Souza da Silva, a housekeeper, said friends urged her to understate her income to qualify for the cash program, but she has refused on principle.

“I see young women in good health — men too — refusing to work,” she said. “That ends up hurting the economy.” Once a Lula voter, she plans to vote for Mr. Bolsonaro on Sunday.

Free health care, but no doctors

Mr. Lula has called Brazil’s free public health system “one of the masterpieces of health care worldwide.’’

That is not a word many in Nanuque would use. Many complained of long waits for specialists in faraway cities, even though a year ago, Mr. Lula launched a program meant to help underserved towns called “Now There Are Specialists.”

“We need the politicians to see us, when it comes to health care,” said Ana Paula Rodrigues dos Santos, 41, who was shopping for the lunches she cooks and sells for $6 each to make a living.

She said she needs her gall bladder removed but explained that the town’s public hospital lacks an intensive care unit, which her doctors have told her she may need since her obesity increases the risk of complications.

She has been on a waiting list at a hospital in a city three hours away for nearly three years, she said.

Ms. dos Santos described herself as an independent who was leaning toward Mr. Bolsonaro.

“It’s been going left, left, left and the left didn’t do anything for Brazil,” she said. “We have to put in new people.”

Prayers and Politics

The right’s increased appeal among voters is not just fueled by growing frustration with Mr. Lula. It is also driven by religion. The percentage of Brazil’s population that is evangelical Christian has tripled since 1991, and members of Evangelical congregations lean heavily conservative.

Dozens of Evangelical churches dot rich and poor neighborhoods in Nanuque, where some pastors preach opposition to abortion and homosexuality.

At New Life Evangelical Church, a relatively wealthy congregation, the pastor, Bishop Robson Merry Teixeira Farias, said he believed nearly all of his 300 members would support Mr. Bolsonaro for president.

Even within less well off congregations, support for Mr. Bolsonaro was still strong, according to pastors and members.

Under Brazilian law, religious leaders cannot make endorsements from the pulpit, but Bishop Merry, as he is known, suggested that preferences can be telegraphed by promoting conservative values that align with specific candidates.

“We do not champion men, we champion causes,” he said.

In a town with no mall or cinema, churches are central to social life, and congregants arrive well dressed and as eager to socialize as to pray.

On Sunday, after church services, they will have a second chance to socialize — at Nanuque’s 21 polling stations.

“As the election approaches, it is the responsibility of leaders” like him, Bishop Merry said, “to pass along their vision.”

“The sheep always try to imitate the pastor,” he added.

Silvia Ribeiro contributed reporting from Rio de Janeiro.

In that first round, Brazilians also gave right-wing politicians control of Congress and governorships across the nation, including four new federal lawmakers with the last name Bolsonaro. (They are the former president’s wife, two other sons and brother.)

The right’s winning streak had already enabled President Trump’s goal to impose greater U.S. influence over Latin America. But Brazil — Latin America’s largest nation in population, area and economy — has been the biggest missing piece in his growing roster of allies in the region.

The Trump administration is bent on exerting new levels of control over the region with tariffs, sanctions, airstrikes, visa revocations, election interventions, an oil blockade on Cuba and the capture of Venezuela’s leader.

It is President Trump’s more aggressive version of the Monroe Doctrine, the 1823 claim of U.S. primacy in Latin America. And the pairing of Mr. Trump’s policy with the right’s ascendance is creating a fundamental shift in the region, particularly when it comes to security.

The Trump administration has made its top priority in Latin America a new war on drugs. The administration has compared fighting the region’s powerful cartels to the war on terror in the Middle East, and has acted accordingly.

The State Department has labeled 21 criminal groups in Latin America as terrorist organizations. The Pentagon has carried out 71 strikes on boats in the waters around Latin America, killing nearly 240 people it claimed were drug traffickers. (Many legal experts consider the strikes illegal.) And last month, American soldiers joined a police operation in Ecuador against a cartel.

That is the sort of cooperation the Trump administration wants to expand. Eighteen Latin American nations have joined a new U.S.-led coalition against cartels, and at least four of them — Colombia, Guatemala, Honduras and Ecuador — have already agreed to joint military operations with the Pentagon.

Mr. Bolsonaro has been an eager Trump supporter for years, as his father was one of Mr. Trump’s top allies during his first administration. Mr. Bolsonaro has already said he would add Brazil to the anti-cartel coalition, called the Shield of the Americas, and work with the United States to fight Brazilian gangs.

He had suggested in social media posts last year that he would welcome U.S. military intervention in Brazil, though he denied that in recent interviews, saying the cooperation would be limited to intelligence. But it was Mr. Bolsonaro who successfully lobbied Mr. Trump to designate two Brazilian gangs as terrorist groups.

It’s not the first time the U.S. and Latin America have tried to fight drug gangs together. But the degree of ideological alignment across the region, as well as the Trump administration’s willingness to intervene militarily, has made this an exceptional moment.

Security experts say the coordination could aid intelligence, especially in tracking criminal financial networks — which have long been a problem for Latin America.

In August, the Pentagon announced a new task force for the Western Hemisphere designed to act as a hub for intelligence and operations among allied countries. And last month, 14 nations followed Washington’s lead and designated various cartels as terrorist organizations.

The largest cartels are effectively multinational corporations, trafficking drugs and laundering money across borders, and so the designations could enable governments to better attack their finances with sanctions.

“You were on your own,” Mr. Trump told his Latin American allies at the United Nations last month. “You’re not on your own anymore.”

At the same time, the Trump administration has signaled that it’s less eager to help leftist governments. That was the case in Colombia before voters there elected Abelardo De La Espriella, a lawyer who has vowed to take an especially hard-line approach to cartels. And as part of a larger diplomatic tiff with Mr. Lula’s leftist government in Brazil, the White House has withheld visas for federal police agents from the country.

Mexico, the other big Latin American democracy still run by a leftist government, has actually expanded its security cooperation with the administration, but the U.S.-Mexico relationship is unique in the region. (Uruguay, whose population is 3.5 million, is the third leftist democracy left in the region.)

There are still questions about whether the counter-cartel coalition can make a difference. Experts say the Pentagon’s boat strikes have hardly slowed the flow of cocaine. And there are few specifics on how countries will actually work together, and what becomes of the effort once Trump is out of power.

There are also questions on what it means for Latin America's citizens and sovereignty. The imbalance in political, economic and military power between the United States and any one Latin American nation is significant, even with Brazil.

Mr. Trump, for instance, tried to intervene in the criminal case against Mr. Bolsonaro’s father, who faced charges for attempting a coup, by imposing 50 percent tariffs on Brazilian products. That effort failed and Jair Bolsonaro was convicted, but Mr. Lula has warned since that Latin America must retain its ability to govern itself in the face of pressure from Washington.

Mr. Bolsonaro, however, has argued that the threat to sovereignty comes not from Mr. Trump but from the cartels. To fight them in Brazil, Mr. Bolsonaro has promised to learn from Nayib Bukele, the president of El Salvador whose authoritarian tactics has drastically lowered crime rates while also drawing complaints of human rights abuses.

In his nation of six million, Mr. Bukele has locked up tens of thousands of young men with little due process, placing many in what he calls “mega-prisons.” Mr. Bolsonaro, who said he has studied Mr. Bukele’s approach, has proposed building five similar prisons, and has also called for lowering the age of criminal responsibility to 16 and chemically castrating rapists and child abusers.

Latin American leaders have increasingly spoken highly of Mr. Bukele’s approach and the results it has yielded, making El Salvador one of the region’s safest nations. Mr. Bukele, who has called himself the world’s coolest dictator, is also, according to polls, one of the world’s most popular presidents.