Democratic backsliding is a pressing concern in the United States, raising questions about the public’s commitment to democratic norms and their willingness to hold politicians accountable for violating them. Scholars have theorized that affective polarization—partisan animosity between Democrats and Republicans—undermines democratic accountability and facilitates norm violations. Yet causal evidence linking affective polarization to explicit support for undemocratic behavior remains limited. This study uses a pre-registered survey experiment to test whether reducing affective polarization leads to greater resistance to undemocratic practices. We implement several depolarization interventions in a large, nationally representative sample of U.S. partisans and assess downstream effects using both a democratic norms battery and a candidate conjoint experiment. By examining whether participants punish candidates who violate democratic norms and/or reduce support for anti-democratic proposals, we provide a strong test of the causal link between affective polarization and democratic backsliding.