Few presidential initiatives have attracted more public ridicule from scientists and engineers than ‘Star Wars’, Ronald Reagan’s 1983 proposal to build a missile defense system that would render the Soviet nuclear arsenal ‘impotent and obsolete’. Scientists found multiple ways of critiquing what Reagan’s vision became: not a working weapons system, but a dramatically escalated research and development program known as the Strategic Defense Initiative (SDI), which stalled arms-control negotiations near the end of the Cold War. This paper examines how scientists crossed discursive boundaries between science and politics as they staged a social movement against SDI: a nationwide boycott of Star Wars research funds. It argues that scientists made discursive choices that furthered their immediate challenge to practices of military-academic research, while still shaping emergent identities in line with existing institutions. Significantly, this account cannot be simply incorporated into existing traditions of research in lay-expert communication. Whereas these traditions suggest that communicative practices either enable or constrain actors, this account shows they simultaneously did both. It advances the notion of ‘discursive choices’ as a concept that may help mediate between structure and agency in studies of public communication with technical experts. This account suggests that an examination of discursive choices may contribute to understanding how expertise is maintained and reconfigured within a particular political culture.