A landslide election win will embolden Claudia Sheinbaum, Mexico's first woman president, to defend her country's interests in sometimes-tense relations with the United States dominated by trade, migration and drugs, experts say.
While the president-elect is expected to be more diplomatic in public than her sharp-tongued predecessor Andres Manuel Lopez Obrador, known by his initials AMLO, in private it could be a different story.
The left-wing former Mexico City mayor apparently plans to be "a tough opponent" for Washington, said Duncan Wood, an expert at the Mexico Institute think tank in the United States.
Sheinbaum, a former student activist who won nearly 60 percent of votes in Sunday's election, pledged in her victory speech to maintain "a relationship of friendship, mutual respect and equality" with the United States.
"And we will always defend the Mexicans who are on the other side of the border," she added.
Migration across the US southern border remains a key flashpoint issue in the United States, making control over the flow "one of the most important levers" Mexico City has in its ties with Washington, Wood told AFP.
He predicts Sheinbaum "will definitely continue to use migration as a bargaining chip."
Sheinbaum's comments "suggest she might advocate for more humane migration policies," said Maria Fernanda Bozmoski, deputy director of the Atlantic Council's Adrienne Arsht Latin America Center, a US-based think tank.
With a sizable majority in Mexico's Congress and a strong mandate from the people, Sheinbaum "may be more difficult (for Washington) to convince than AMLO once was," she told AFP.
Activists have criticized Lopez Obrador's government for cooperating with Washington by receiving asylum seekers expelled by the United States or detaining and deporting migrants in transit.
US President Joe Biden, in a dramatic bid to neutralize one of his political weak spots ahead of the November election, announced new measures this week that would temporarily shut the border to asylum seekers when illegal crossings surge.
Lopez Obrador said afterward that Mexico was interceding with the governments of Cuba and Venezuela so that the United States could deport undocumented migrants directly to those countries.
And in the Mexican capital, immigration agents raided and cleared a makeshift migrant camp on Wednesday night while people were asleep in their tents.
US-bound migrants passing through Mexico City voiced hope that a Sheinbaum presidency would make their lives easier.
"A human being cannot treat another human being like an animal," said Arley Canelon, a 56-year-old Venezuelan who hopes to join his four children in the United States.
The Mexican government could at least provide migrants with places to eat and stay along the way, he told AFP.
Carmen Chacon, a 23-year-old Venezuelan traveling with her husband and two children, appealed to Sheinbaum to "do everything possible to help migrants."
"We don't want to stay here. We're just passing through," she added.
Washington is also expected to push Sheinbaum for action in the fight against Mexican cartels' trafficking of drugs such as fentanyl, a synthetic opioid behind a US overdose epidemic.
Wood said there would be an "enormous amount of pressure" from both the White House and US Congress on the issue, "particularly in an election year."
The economy is another key issue, with Mexico recently replacing China as the United States' biggest trade partner.
A North America free trade agreement that was revamped in 2020 is due to be reviewed in 2026, potentially leading to disagreements, experts said.
If Sheinbaum's ruling party uses its big win to carry out controversial reforms damaging to the business and investment climate, experts say tensions could rise.
Such changes "could be a potential powder keg for 2026," Wood said.
Mexican stocks and the peso fell sharply after Sheinbaum's victory as investors fretted about proposed constitutional changes such as electing judges by popular vote.
Sheinbaum, a passionate leftist, on Thursday posted a picture of herself meeting Sergio Mendez, head of the Mexican arm of US investment giant BlackRock.
A huge wildcard is the possible return of Donald Trump to the White House if he defeats Biden in November -- and how he would treat Sheinbaum.
"I think he'll assume that he can push her around and she's going to have to have a very strong backbone to prevent that," said Pamela Starr, a professor at the University of Southern California.
Wood said it was hard to predict how Trump would behave.
"Trump is enigmatic. He's his own man. He managed to forge a very positive relationship with AMLO, despite the enormous differences between them," he said.
