"My promise is that CDC will continue to follow the science as our guide," Rochelle Walensky, director of the Centers for Disease Control and Prevention, told senators last week. While Walensky thinks the CDC already is doing that, her premise is contradicted by the agency's history of arbitrary, dubious and ever-changing advice about COVID-19. Early in the pandemic, the CDC, together with the Food and Drug Administration, disastrously bungled the rollout of virus tests, making it impossible to curtail the spread of COVID-19 through contact tracing. Its obstruction of independently produced tests was coupled with irrationally narrow guidelines that initially...