All the participants in the Great Debate took for granted the importance of radio and made it central to their efforts. While they generally worked within radio’s rules, they also tried to work around or even break those rules, setting the stage for changes that ultimately altered the way media managed American political discourse. This study breaks with traditional accounts that see radio as an industry biased in favor of interventionism. Rather, radio fully aired the opposing positions in the debate. It nonetheless failed to resolve fully their differences. Despite the initial enthusiasm for radio’s educational potential, participants on both sides came to doubt their conviction that radio could change minds. Radio increasingly became a tool to rally existing supporters more than to recruit new ones. Only events ended the debate over US involvement in World War II. The larger question—of what role the US should play in world affairs—remained.