Re Mexico's leverage
From Washington Post article:
While the United States is the stronger power, Mexico is not without leverage if this dispute escalates. Top economic officials have already said that Mexico would “mirror” any additional taxes or tariffs that the United States imposes. Former officials have said that Mexico could also tax corporate profits from the many American companies with operations in Mexico.
Outside of the economic realm, Mexico also has plenty of cards to play in negotiations with Trump. Last year, Mexico deported nearly 150,000 migrants bound for the United States, most of them from Central America. Without this cooperation, officials predict that the number of migrants turning up at the U.S. border could double.
At the border, Mexican officials have been important partners on a variety of tasks, including gathering intelligence on drug cartels and facilitating food inspections, often working side by side with their U.S. counterparts. Mexico has also apprehended foreigners from other countries that pose a potential national security threat and has allowed U.S. authorities access to them. That cooperation could change.