question: Rampant partisanship in the United States may be the largest obstacle to the reduced social mobility most experts see as critical to limiting the spread of the COVID-19 pandemic. Analyzing a total of just over 1.1 million responses collected daily between 4 April and 10 September reveals not only that partisanship is more important than public health concerns for explaining individuals' willingness to stay at home and reduce social mobility but also that the effect of partisanship has grown over time-especially among Republicans. All else equal, the relative importance of partisanship for the increasing (un)willingness of Republicans to stay at home highlights the challenge that politics poses for public health.