For much of the post-Cold War era, Brazilian diplomats complained that Washington paid too little attention to Latin America's largest country. Not anymore.

As Brazil's presidential campaign begins next week, what began as a two-man race between President Luiz Inácio Lula da Silva and Flávio Bolsonaro, the son of jailed former President Jair Bolsonaro, has increasingly become a three-way fight involving President Trump.

Da Silva has accused Trump of trying to interfere in the October election to return the Brazilian right to power, while tit-for-tat visa disputes and U.S. tariffs have plunged relations between the Western Hemisphere's two most-populous nations to their lowest point in years.

Trump's "improper interest in interfering in the next presidential election" is now clear, Brazil's government said late Tuesday after Washington revoked the visa of its ambassador to the U.S. The move came after Brasília withheld approval of Trump's own ambassadorial nominee and recently denied entry to several U.S. diplomats it said were planning to meddle in the vote. The State Department has called that accusation a "baseless lie."

From Argentina to Peru, South America's political pendulum has swung sharply to the right over the past few years, with conservative leaders increasingly aligning themselves with Trump. Now the battle over the region's political future has come down to Brazil, which is hurtling toward one of its closest and most consequential elections in decades.

Da Silva, 80, is seeking re-election for the leftist Workers' Party. A victory would give him a fourth presidential term after governing from 2003 to 2010 and again since 2023, cementing one of the longest political careers in modern democratic history and leaving Brazil as the last major left-led economy in South America.

Flávio Bolsonaro, a 45-year-old senator, is running as the political heir to his father, who is serving a 27-year prison sentence for plotting to overturn the 2022 election. Allied with Trump and Argentine President Javier Milei, Bolsonaro's eldest son is seeking to prove the Bolsonaro movement can outlive the man who created it.

Polls suggest a razor-thin race. The latest Datafolha survey gives da Silva a narrow lead over Bolsonaro, though pollsters have repeatedly underestimated right-wing support in recent elections. With former Goiás Gov. Ronaldo Caiado, Missão party leader Renan Santos and other conservative candidates polling in the single digits, analysts expect their supporters to overwhelmingly back the younger Bolsonaro in a likely Oct. 25 runoff, setting up a close finish.

Public security, healthcare and the cost of living are expected to dominate the campaign. But the election will also serve as a test case of how far Trump and an increasingly coordinated global right are willing to go to reshape Latin America's political landscape, political scientists say.

"Brazil has in fact become a thorn in the side -- and a problem -- for U.S. foreign policy," said Rafael Cortez, a political scientist at São Paulo-based consulting firm Tendências. Washington views Brazil as challenging U.S. influence in its own backyard through its leadership role in the Brics -- an 11-member group of emerging economies -- and its deepening ties with China, he said. "Brazil in 2026 risks becoming a kind of new Cuba of 1959" for U.S. policymakers, he said, reviving geopolitical concerns reminiscent of the Cold War.

Trump has already tested the limits of U.S. diplomatic involvement in the region. In Argentina, his administration extended a $20 billion financial lifeline in the form of a currency swap to Milei, giving his ally a much-needed political boost less than three weeks before last year's midterm elections.

In Brazil, the effort has been bolder. Last July, Trump announced 50% tariffs on Brazilian imports -- the highest imposed on any country -- and explicitly linked them to pressure on Brazilian authorities to drop criminal proceedings against Jair Bolsonaro.

The Bolsonaros have also actively sought Trump's involvement. Eduardo Bolsonaro, Flávio's younger brother, moved to the U.S. last year to lobby conservative allies over his father's prosecution.

But da Silva has also embraced the confrontation, some analysts say. Long known as a pragmatic diplomat who has favored dialogue on the world stage, the leftist stalwart has found political advantage in his clash with Trump, casting himself as the defender of Brazil's sovereignty and tapping in to deep-rooted sensitivities over foreign interference.

Even before Washington entered the picture, Brazil was already set for one of its most tense elections in decades. The race marks a striking reversal of fortunes for the country's two dominant political movements. With Jair Bolsonaro under house arrest and barred from running, Flávio is now left to carry his political banner. A Flávio victory could pave the way for amnesty for his father and hundreds of his supporters convicted over efforts to overturn the last election.

Eight years ago, it was da Silva who was behind bars on corruption convictions, desperately trying to keep his political movement alive through a stand-in as Bolsonaro swept to power in the 2018 election.

But after nearly a decade of bitter polarization, the anger that once energized both camps has increasingly given way to fatigue among ordinary Brazilians. Although voting is compulsory, the penalty for not doing so costs less than a bus fare. About one in five voters skipped the first round of the last presidential election -- the highest abstention rate since 1998.

This year's election may ultimately be decided by which candidate voters hate the least.

Even on the left, some question whether da Silva is fit for another term given his age. Centrist voters also remain haunted by his links to Brazil's sprawling Car Wash corruption scandal, a multibillion-dollar kickback scheme uncovered in 2014. Although da Silva's convictions were later annulled, many Brazilians remain unconvinced that one of the country's shrewdest politicians knew nothing about the billions stolen under his governments.

Meanwhile, Flávio Bolsonaro has sought to present himself as a more polished politician than his father, but his candidacy carries memories of the chaos that followed the 2022 election, culminating in supporters storming government buildings on Jan. 8, 2023. He has struggled to unite the center-right, with the powerful União Progressista alliance opting for neutrality rather than endorsing his candidacy.

A public feud with his stepmother, former first lady Michelle Bolsonaro -- one of the conservative movement's most popular figures among women and evangelical voters -- has also alienated some voters. Meanwhile, a leaked audio recording and past corruption allegations have raised fresh questions about his ethics. Flávio has denied wrongdoing.