The White House needed a comprehensive testing strategy for staff and visitors if they were going to rely on diagnostic screening as the sole tool to keep the virus from spreading inside the West Wing and not combine testing with masks and distancing. The White House instead deployed tests that are known to be prone to false negatives when they are used to screen an asymptomatic population.

People advising the president have told him, even recently, that herd immunity is at hand and that masks don’t work. The latest rosy scenario in administration circles holds that most Americans harbor T-cells from fighting other coronavirus infections that are programmed to attack Covid, and thus the epidemic is much closer to ending than mainstream scientists believe.

Every theory should be explored, but wishful thinking isn’t sound policy. The present situation calls for a balanced caution—not for shutting down the economy but for avoiding large gatherings, covering faces, and keeping a close eye on the still-rampant spread of the virus.