"Possibly, local stay-at-home policies attenuate the observed partisan differences in physical distancing because these policies send out clear signals about the dangers of COVID-19. In line with this reasoning, we predicted that state-level stay-at-home orders would potentially reduce the observed partisan differences. Our data did not support this prediction. The link between voting for Trump and reduced physical distancing was actually stronger when stay-at-home orders were in effect, as evidenced by negative interactions between vote gap (with higher values indicating greater pro-Trump lean) and state policy: Bmovement = −0.017, 95% CI [−0.022, −0.013], P < 0.001 and Bvisitation = −0.009, 95% CI [−0.016, −0.001], P = 0.030. These results align with recent work finding that Democratic counties responded more quickly to stay-at-home orders than Republican counties at the start of the pandemic. We considered the possibility that variability in state stay-at-home policies explains our findings rather than county-level partisanship. For instance, stay-at-home orders may have been more stringent and remained in place longer in Democratic states or in states with Democratic governors, in turn leading Republican-leaning counties (which are more common in Republican states) to exhibit less physical distancing. Three supplementary analyses argued against this possibility, however. First, our results remained when adjusting for whether state policies were in effect on a specific date, state governors’ political affiliation, and interactions between these variables and partisanship. Second, we also confirmed that our results remained when adding specific state policies (including closing restaurants, closing childcare, closing K–12 schools, closing non-essential business more generally, and closing religious institutions/gatherings), and the interactions between these policies and governor political party and partisanship, to our models. And third, while there was some variation in our findings between states, most states were in line with the population average of the observed partisan differences. In sum, though differences in state policies contribute to variation in county-level physical distancing, our results indicate that county-level partisanship nonetheless explains unique variance in physical distancing."