President Claudia Sheinbaum is detaining more migrants, seizing more fentanyl and positioning her country as a key ally against China. But the U.S. stance has shifted, too.

How will Mexican leaders respond if, as expected, Trump pressures them to accept deportees from third countries? 'Mexico is in a really tough spot.'

All along the 2,000-mile border, business leaders, border agents, migrants and their advocates are bracing for change in U.S. policies on trade and immigration.