When submitted to popular ratification, new constitutions tend to be approved. Chilean voters, however, rejected the proposal put forward by the country’s Constitutional Council in 2023. This article examines the reasons for this outcome. Leveraging an original conjoint experiment exploring voter preferences across four policy areas, we demonstrate that most voters disfavored a proposed clause protecting unborn life, which would have likely restricted access to abortion. Despite general support for other provisions in the draft, opposition to the abortion clause proved pivotal. Our analysis underscores the risks of partisan constitutional proposals dependent on the median voter for approval and highlights the importance of abortion as a mobilizing issue in contemporary democracies. The study also suggests that right-wing drafters miscalculated voter support, even as moderate members attempted to amend the controversial clause, showcasing the limitations of compromise-inducing rules when one ideological bloc controls the drafting process.