There were some new hires but across 14 agencies operating in sectors like health, weather and environment, the overall picture was a net exodus of more than 4,000 highly trained workers. That shrinking hinterland of scientific expertise is evident in recent pronouncements: the repeal of the “endangerment” ruling that greenhouse gases threaten human health, which underpins climate legislation; the downgrading of pandemic preparedness research by the health agency tasked with responding to infectious diseases; and the refusal by regulators this month to review Moderna’s new mRNA flu vaccine.