Until a few decades ago, the popular but falsely reassuring belief was that babies in the womb were perfectly protected by the placenta and that children were just “little adults,” requiring no special protections from environmental threats. We now know that a host of chemicals, pollutants and viruses readily travel across the placenta from mother to fetus, pre-polluting or pre-infecting a baby even before birth.

Toxic chemicals like lead, certain air pollutants, pesticides, synthetic chemicals and infectious agents like Zika can derail the intricate molecular processes involved in a fetus’s healthy brain development. So can physical and social stress experienced by the mother.

At a time when we should be spending more on research and prevention of those threats, President Trump would do the opposite. He would cut the budget of the Environmental Protection Agency by 31 percent, including cuts to scientific work on chemical safety. He would slash money for biomedical research and programs to fight outbreaks of infectious disease. We need more spending in those areas, not less. We need more testing of chemicals before they are marketed, not less.

Toxic exposures are shockingly prevalent. Analysis of biomonitoring data from the Centers for Disease Control and Prevention finds dozens of toxic chemicals, pollutants and metals in pregnant women, many of which are also found in cord blood of newborns. These include pesticides sprayed in inner-city buildings and on crops, flame retardants used in furniture, combustion-related air pollutants from fossil-fuel-burning power plants and vehicles, lead, mercury and plasticizers. All have been shown in epidemiologic studies in the United States and elsewhere to be capable of damaging developing brains, especially while babies are exposed in utero or in their early life.