This essay examines how medical rhetorics helped justify the recent torrent of anti-trans legislation. Beginning with the “legitimacy wars” between psychiatry and psychology, I trace how competing disciplines established their own expertise by denying trans patients’ agency and self-knowledge. After identifying the “trans trickster” trope that emerges from these rhetorics, I trace how the trans trickster haunts arguments used to ban gender-affirming health care and sports participation for trans youth. I draw from sociologist Ian Hacking’s “looping effects” to explain how medical logics affect public perception and how those understandings loop back into medical research. The binary, linear models of gender transition established by trans medicine helped justify cisnormative policies around transgender identity, which in turn restricted further scientific inquiry such that more imaginative gender formations remain illegible. To conclude, I argue that medical paradigms work in relation with trans imagination would expand scientific explorations of human diversity, and that those understandings too could loop through public policy and perception.