Around the world, would-be authoritarian leaders have convinced their supporters to vote away the democracies they claim to cherish. How is this possible? We argue that simply fearing that opposing partisans support democratic backsliding can lead individuals to support it themselves. Would-be authoritarians may then be able to start a self-reinforcing dynamic of democratic backsliding by fostering these fears, which then generate exaggerated fears on the other. Using observational and experimental studies (N=4,400), we present four findings consistent with this account: Republicans and Democrats (1) overestimate opposing partisan willingness to break democratic norms; (2) will support their party breaking democratic norms themselves to the extent that they overestimate willingness by the other side; (3) that experimentally correcting this overestimation reduces support for breaking norms, and (4) increases the likelihood of voting for candidates that uphold democratic norms. Our findings suggest that we can foster democratic stability even in a highly polarized society using interventions that simply correct misperceptions about opposing partisans’ commitment to democratic norms