2. Mexico and the U.S. made progress toward a deal to avoid tariffs that would require migrants to seek asylum in the first safe country they enter. Above, an immigration checkpoint in Tapachula, Mexico.

Mexico has also pledged to send thousands of troops to the border with Guatemala, if a deal is reached, and could also expand an American program in which asylum seekers wait in Mexico while their cases are processed. Any final agreement would await President Trump’s return from Europe.

If Mr. Trump does impose the tariffs, it would be an atypical use of his emergency powers. Here’s what that means, and here are the states that would be hardest hit.