Alberto Fernández's victory in Argentina's presidential election is set to cement a rift between South America's largest nations, and suggests regional turbulence could extend for years.
The Frente de Todos leader and his far-right Brazilian counterpart Jair Bolsonaro have antagonised each another since August, and their statements since Sunday's vote signal that neither plans to relent.
In his victory speech, Fernández declared that Brazil's leftist former president Luiz Inácio Lula da Silva – Bolsonaro's nemesis – is unjustly imprisoned and demanded his freedom.
Bolsonaro, meanwhile, told reporters during a visit to Abu Dhabi that Argentina had "chosen poorly" and that he didn't intend to offer his congratulations.
Brazil and Argentina are the biggest members of the Mercosur trade customs union that this year celebrated reaching a free-trade accord with the European Union after two decades of negotiations. The deal appeared to be a bonanza for South American farm products, while French farmers feared it would swamp them with cheap imports, particularly beef and poultry.
Brazil's economic policymakers hailed it as a milestone in opening their closed economy, claiming it will have a total economic impact of US$87.5 billion in Brazil through 2035. Fernández, for his part, has expressed scepticism of deal.
Partly as a result of Mercosur, the nations are also heavily reliant on one another for trade and political friction could complicate the growth of job-creating trade and investment.
Fernández will begin his four-year term in December and Bolsonaro's first term finishes in December 2022, meaning they will simultaneously hold office for at least three years.
Oliver Stuenkel, a professor of international relations at the Fundação Getúlio Vargas, a university in São Paulo, said open hostility between the two reflects them playing to radical wings of their respective alliances to ensure domestic support. That strategy will make it difficult for pragmatists on either side of the border to defuse the imbroglio, notwithstanding their economic interdependence.
"When you don't have a personal, workable relationship, anything can become a fire. When there's no trust on top, it's hard to put out fires. There will be disagreements," Stuenkel said by phone. "There are doubts about whether Fernández and Bolsonaro will be on talking terms.
"Bolsonaro didn't call to congratulate; these are petty, small politics and the real big questions that the region faces aren't being discussed or addressed."
South America in recent years saw a surge of centre-left leaders known as the 'Pink Tide' retreat, which was mistakenly interpreted at the time as right-wing politicians regaining ground, according to Christopher Garman, Eurasia Group's managing director for the Americas. In fact, the shift represented widespread dissatisfaction with the overall status quo, further evidenced in recent weeks by massive street protests in Ecuador and Chile.
"It's not that voters went right; they just kicked out incumbents. And they remain angry. It wasn't a policy and ideological move when it came to voter demands," Garman said. "That difficult public opinion environment remains, and there is variable capacity of governments to be able to navigate this. It's the underbelly of difficult middle-class politics across the region."
Countries' positions toward Venezuela's socialist government also divide the region. Venezuela is in the throes of catastrophic depression that's prompted food and medicine shortages, plus the exodus of millions.
Fernández's party was long allied with Venezuela's leaders and he is widely expected to withdraw from the Lima Group, which includes Brazil, that doesn't recognise the legitimacy of Venezuelan President Nicolás Maduro.
Bolsonaro in August warned a prospective Fernández government would resemble that of Maduro, and referred to him and his running-mate, former President Cristina Kirchner, as "red bandits."
Brazil's Foreign Minister Ernesto Araújo said on Twitter on Monday that Fernández's win sends "the worst possible signals. Trade closure, a retrograde economic model and support for dictatorships." He added Brazil will be pragmatic in its defence of the country's principles and interests.
Argentina and Brazil falling out would have broader implications, as it's impossible to have real debate about South American integration or face up to regional challenges if they aren't on the same page, Stuenkel said.
"It's clearly the most unpredictable period since democratisation in the late 1980s. Starting then, there was consensus that more cooperation was better, and that's no longer the case," he said.