A digital sign directs people to drive-through coronavirus test sites on March 28, 2020, in Stony Brook, New York. | John Paraskevas/Newsday via Getty Images

The US never fixed the core causes of its testing problem. So it’s now seeing the same kinds of issues pop up again.

Covid-19 testing in the US improved dramatically over the first half of 2020, but things now appear to be breaking down once more as coronavirus cases rise and outstrip capacity — to the point that the mayor of a major American city can’t get testing quickly enough to potentially avoid spreading the virus.

“We FINALLY received our test results taken 8 days before,” Atlanta Mayor Keisha Lance Bottoms tweeted July 8. “One person in my house was positive then. By the time we tested again, 1 week later, 3 of us had COVID. If we had