President Joe Biden’s attempts to grapple with a record number of migrants are keeping the role of border enforcement at the center of the U.S. immigration debate.

The swift development of effective vaccines against COVID-19 was an unprecedented scientific achievement. But production challenges, vaccine nationalism, and new variants have all presented hurdles.

U.S. space exploration inspired a generation of students and innovators, but NASA’s role has diminished, and the number of global space competitors is growing.

Here’s how different health-care systems, including single-payer and government-run, have contended with the coronavirus.

The federal agency has a broad mandate to protect Americans’ health and an expansive global reach. But the COVID-19 pandemic has been one of its most daunting challenges.