For generations, experts argued that American politics needed cohesive parties to function effectively. Now many fear that strong partisan views, particularly hostility to the opposing party, are damaging democracy. We address this concern with a nuanced evaluation of when and how partisan animosity matters in today’s highly charged, dynamic political environment, drawing on panel data from some of the most tumultuous years in recent American history, 2019 through 2021. Partisanship powerfully shapes political behaviors, but its effects are conditional, not constant. Instead, it is most powerful when politicians send clear signals and when an issue is unlikely to bring direct personal consequences. In the absence of these conditions, other factors often dominate decision-making. Hence, while partisan hostility has degraded US politics—for example, politicizing previously non-political issues and undermining compromise—it is not in itself an existential threat. American democracy depends on how politicians, more than ordinary voters, behave.