How can the U.S. solve its coronavirus testing troubles?

Since the early days of the coronavirus pandemic, the U.S. has struggled to keep up with the level of testing needed to track, let alone contain, the virus.

When the initial phase of infection struck, limited supply meant tests were reserved for only the sickest patients, so mild and asymptomatic cases went undetected. The U.S. has dramatically increased testing capacity since then — from about 100,000 tests a day in March to roughly 800,000 by late July. But even those numbers are proving to be insufficient in some parts of...