President Trump on Thursday cited the growing water debt that Mexico owes the United States under a treaty governing the use of the countries’ shared rivers.

© Daniel Berehulak for The New York Times

In a world lurching rightward, Mexico’s president offers progressives hope.

President Trump has offered a mix of reasons for upending global trade relations, baffling and angering America’s biggest trading partners.

Prime Minister Justin Trudeau of Canada warned that the Trump administration’s tariffs were leading to a trade war. Mexico’s leader vowed to impose countermeasures on Sunday.

Aiming to appease President Trump, Mexico is hitting China with tariffs, handing cartel leaders over to the United States and using C.I.A. intelligence to hunt down others.