"We also linked the observed partisan differences in physical distancing to COVID-19 infections and fatalities. Mediation analyses revealed that reduced physical distancing in counties was linked to a subsequent increase in COVID-19 infection and fatality growth rates roughly 17–23 and 25–31 days later, respectively. These results imply that Trump-leaning counties could have curbed their infection and fatality growth rates if they had distanced to the same degree as Clinton-leaning counties did. Such findings provide evidence that partisanship in the United States during the COVID-19 pandemic may have had meaningful—and severe—health-related consequences. Partisanship may therefore be an important risk factor during a public health crisis, one that is probably especially relevant when the electorate is highly polarized and leaders fail to generate bipartisan support for public health measures. The observed partisan differences appear to be relatively strong as well as highly robust. Partisanship was more strongly associated with physical distancing than most of the covariates included in our models, including more traditionally examined health-related variables such as economic and social indicators. The relationship between partisanship and distancing also held after statistically adjusting for numerous control variables, and for interactions between partisanship and these control variables. The robustness of these findings is consistent with findings from independent research groups who have also observed links between partisanship and physical distancing using different data sources. Taken together, these findings provide a more complete picture of partisanship during a pandemic and establish it as an important risk factor for COVID-19 in the United States."