President Trump withdrew from the Obama-era nuclear accord in 2018, saying it was the worst deal ever. But Iran responded with an enrichment spree that haunts the negotiations to this day.
A once-robust H.I.V. treatment and prevention system, credited with saving hundreds of thousands of lives, has begun to crumble.
Blocking the narrow waterway between Russia and Alaska could help stabilize a vulnerable system of ocean currents, scientists found in a study.
A new study found that a pachyderm skeleton, dismissed for decades as unimportant, offers evidence of careful planning, teamwork and a calculated kill.