On February 5th, sixteen days after a Seattle resident who had visited relatives in Wuhan, China, was diagnosed as having the first confirmed case of covid-19 in the United States, the Centers for Disease Control, in Atlanta, began sending diagnostic tests to a network of about a hundred state, city, and county public-health laboratories⁠. Up to that point, all testing for covid-19 in the U.S. had been done at the C.D.C.; of some five hundred suspected cases⁠ tested at the Centers, twelve had confirmed positive. The new test kits would allow about fifty thousand patients to be tested, and they would also make testing much faster, as patient specimens would no longer have to be sent to Atlanta to be evaluated.

The kits were shipped in small white cardboard boxes. Inside each box were four vials, packed in stiff gray foam⁠, which held the necessary materials, known as reagents, to run tests on about three hundred⁠ people. Before a state or local lab could use the C.D.C.-developed tests on actual patients, however, it had to insure that they worked the same way they had in Atlanta, a process known as verification. The first batch of kits, sent to more than fifty state and local public-health labs⁠, arrived on February 7th. Of the labs that received tests, around six to eight were able to verify that they worked as intended. But a larger number, about thirty-six of them, received inconclusive⁠ results from one of the reagents. Another five, including the New York City and New York State labs, had problems with two reagents. On February 8th, several labs reported their problems to the C.D.C. In a briefing a few days later, Nancy Messonnier, the director of the National Center for Immunization and Respiratory Diseases, said that although “we hoped that everything would go smoothly as we rushed through this,” the verification problems were “part of the normal procedures⁠.” In the meantime, she said, until new reagents could be manufactured, all covid-19 testing in the United States would continue to take place exclusively at the C.D.C⁠.

The public-health-laboratory network was never intended to provide widespread testing in the event of a pandemic. To offer tests to anyone who wanted them, as President Trump did, on March 6th, was always going to require commercial testing facilities to come on line. Still, the three-week delay caused by the C.D.C.’s failure to get working test kits into the hands of the public-health labs came at a crucial time. In the early stages of an outbreak, contact tracing, isolation, and individual quarantines are regularly deployed to contain the spread of a disease. But these tools are useless if suspected cases of a disease cannot be tested. The void created by the C.D.C.’s faulty tests made it impossible for public-health authorities to get an accurate picture of how far and how fast the disease was spreading. In hotspots like Seattle, and probably elsewhere, covid-19 spread undetected for several weeks, which in turn only multiplied the need for more tests. “Once you’re behind the eight ball, it’s very hard to catch up,” Alberto Gutierrez, the former head of the F.D.A. Office of In Vitro Diagnostics and Radiological Health, which regulates tests, told me. “The problem was that containment was not done very well. At this point, we’re looking at exponential growth, and we need to figure out how to meet an exponential demand.”

The covid-19 tests use polymerase chain reaction, or PCR, a technology for whose invention the biochemist Kary Mullis won the Nobel Prize, in 1993. PCR is highly sensitive to contamination and other faults, which is why the verification step is necessary to insure accurate results. And yet while the reagent problems were, in their way, a fairly ordinary technical hiccup—Messonnier, at the C.D.C., was not spinning the situation—the cascading effects that they’ve had on the country’s covid-19 preparations suggest a much larger problem with the way the United States has structured its pandemic response. That problem was exacerbated by a President who has simultaneously underplayed the severity of the outbreak and overpromised the means available to fight it.