Few places in the Americas stand to be as jolted by a new Trump presidency as Mexico, the nation of nearly 130 million people that the president-elect made the target of numerous threats during his campaign.

Now as Donald Trump prepares to return to the White House, Mexico finds itself again at the center of his aggressive stances on trade, immigration and drug trafficking.

Despite a sharp decline in border crossings this year after Mexico emerged as an enforcer of the Biden administration’s migration restrictions, Mr. Trump’s campaign vows suggest a complex and contentious road ahead.

He is promising steep tariffs, renegotiated trade deals and even military intervention against cartels. How Mexico’s leaders, under President Claudia Sheinbaum, navigate this landscape will be pivotal, potentially setting the tone for North American diplomacy for years to come.

Here are four things to know about how a newly elected Mr. Trump might reshape the United States’ relations with Mexico.

1. Trump has vowed to bolster border security and deport millions of undocumented migrants.

Like his predecessor, Mr. Trump has big plans for remaking America’s immigration system. But their visions could not be more different.