Both the Food and Drug Administration and the National Institutes of Health lack permanent leaders. Mr. Biden’s health secretary, Xavier Becerra, has been criticized for his low profile. And on Monday, his science adviser, Dr. Eric S. Lander — the first such adviser to serve in the cabinet — resigned after acknowledging that he had bullied his colleagues.

Dr. Lander’s departure leaves a particularly big hole. He was in charge of the “cancer moonshot,” an initiative to cut death rates from cancer in half over the next 25 years, and was behind a new pandemic preparedness plan that the White House has likened to the Apollo mission.

Dr. Lander was also a driving force behind Mr. Biden’s proposal to create a new agency to propel innovation in medical research. Modeled after the Defense Advanced Research Projects Agency, the proposed agency, known as ARPA-H, was the subject of a House committee hearing on Tuesday. Dr. Lander, who was supposed to be the key witness, was not there.