Medetomidine, a veterinary sedative mixed into fentanyl, has sent thousands to hospitals, not only for overdose but for life-threatening withdrawal. It is spreading to other cities.

© Hannah Yoon for The New York Times

Readers respond to a guest essay about America’s fentanyl problem. Also: A dark echo at Penn.

Everything the Trump administration is doing to stop the flow of drugs is just making the problem worse.

China will require licenses for export of 13 chemicals used to make the deadly drug, another indicator of thawing tensions between the world’s two largest economies

The president’s trade truce with China has lowered U.S. tariffs to a level that could pause a longer-term effort to reduce America’s dependence on Beijing.

Some analysts say Beijing won a major victory in its trade talks: Getting the U.S. to withdraw a national security measure that previously was not under discussion.

The highly anticipated event covered a lot of ground on tariff and trade barriers, but questions remain about reaching a lasting accord.

The two leaders reached an agreement on fentanyl, some tariffs and rare earths, at least for a year. But even as the global trade picture cleared a little, Mr. Trump spurred new worries about nuclear proliferation.

Negotiators announced on Sunday they had preliminarily agreed on several issues ahead of an expected meeting between President Trump and Xi Jinping this week.