Context: Social distancing is an essential but economically painful measure to flatten the curve of emergent infectious diseases. As the novel coronavirus that causes COVID-19 spread throughout the United States in early 2020, the federal government left to the states the difficult and consequential decisions about when to cancel events, close schools and businesses, and issue stay-at-home orders.

Methods: We present an original, detailed dataset of state-level social distancing policy responses to the epidemic, then apply event history analysis to study the timing of implementation of five social distancing policies across all fifty states.

Results: The most important predictor of when states adopted social distancing policies is political: All else equal, states led by Republican governors were slower to implement such policies during a critical window of early COVID-19 response.

Conclusions: Continuing actions driven by partisanship, rather than public health expertise and scientific recommendations, may exact greater tolls on health and broader society.

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