It is not a question of whether babies will be born in the United States with Zika-related microcephaly — it is a question of when and how many. For years to come, these children will be a visible, human reminder of the cost of absurd wrangling in Washington, of preventable suffering, of a failure of our political system to respond to the threat that infectious diseases pose. … These are not random lightning strikes or a string of global bad luck. This growing threat is a result of human activity: human populations encroaching on, and having greater interaction with, habitats where animals spread these viruses; humans living more densely in cities where sickness spreads rapidly; humans traveling globally with increasing reach and speed; humans changing our climate and bringing disease-spreading insects to places where they have not lived previously. From now on, dangerous epidemics are going to be a regular fact of life. We can no longer accept surprise as an excuse for a response that is slow out of the gate.