The United States reached a milestone, of sorts, when last week the Food and Drug Administration approved the first treatment for COVID-19. The drug is called Veklury, although most people know it by its scientific name, remdesivir. On Wednesday, its manufacturer, Gilead Sciences, said that remdesivir, which has been authorized for emergency use since the spring, had brought in $873 million in revenues so far this year and that it was the company’s second-best-selling drug in the third quarter, behind its HIV drug, Biktarvy. But the FDA’s decision to grant the drug full approval — which means the company can begin broadly marketing it to doctors and patients — has puzzled several outside experts, who say that it may not deserve the agency’s stamp of approval because it is, at best, a mediocre treatment for COVID-19, the disease caused by the coronavirus. And they have questioned whether Gilead deserves to pocket potential billions from the drug when the federal government has played