First, many Republicans are visceral if not doctrinal libertarians. They understand freedom as being left alone to make their own choices, and they resent being told what to do. They implicitly reject John Stuart Mill’s distinction between actions that affect only ourselves and those that affect others. From their perspective, mask mandates restrict freedom, whatever their purported social justification, and so does pressure to get vaccinated... Second, an increasing number of Republicans are populists who bristle at what they see as elite condescension toward ordinary citizens. When medical experts assure us that the Covid-19 vaccines are safe and effective, many Republicans wonder how they can be so sure about medicines that were developed so quickly. Shifting expert views on mask mandates and modes of disease transmission have bolstered these doubts. Third, for more than a century, white evangelical Protestants have had a tense relationship with modern science, which they see as challenging core tenets of their faith. They are less likely than other Americans to take “follow the science” as their benchmark.