Public health disparities provide an important lens for understanding social and political change in the USA. Using individual-level medical data and death records, this study shows that conservative Americans experienced worsening health and higher mortality than liberals during the 2010s. Here we find evidence consistent with two potential mechanisms. First, demographic realignment within political coalitions brought less healthy individuals into the conservative camp. Yet by the 2020s, demographic change, public policy and COVID-19 do not fully account for the widening gap in mortality rates. Public opinion data are consistent with a second mechanism: declining trust in medical professionals among right-leaning individuals, including lower willingness to seek care, follow clinical advice or believe in medication effectiveness, even for issues unrelated to COVID-19. These patterns suggest that growing ideological divides in health behaviours are leaving conservative Americans increasingly vulnerable to preventable health risks. Using individual-level medical data and death records, this study finds that conservatives in the USA experienced worse health and higher mortality than liberals during the 2010s. No significant gaps in biomarkers or mortality were present before the 2010s.