This study revisits a critical juncture in the development of national health insurance (NHI) in the United States in the post-World War II era. We investigate the role of the American Medi- cal Association (AMA) which financed a campaign against NHI that was directed by the coun- try’s first political public relations firm, Whitaker & Baxter’s Campaigns, Inc . The Campaign had two key components: (1) physician outreach to patients and civic organizations; and (2) mass advertising that tied private insurance to “freedom” and “the American way.” We bring to- gether archival data from several novel sources documenting Campaign strategy and intensity. We find a one standard deviation increase in Campaign exposure explains about 20% of the increase in private health insurance enrollment and a similar decline in public opinion support for legislation enacting NHI. We also find evidence that the Campaign influenced the narrative for how legislators described health insurance, leading Republicans to use speech similar to the Campaign. These findings suggest the rise of private health insurance in the U.S. was not solely due to wartime wage freezes, collective bargaining, or favorable tax treatment. Rather, it was also enabled by an interest group-financed Campaign that used ideology to influence the behavior and views of ordinary citizens.