Political polarization affects the social trust and norms upon which democracy is built. In a pre-registered study using a representative sample of the United States (N = 1000), we investigated how two conceptualizations of truth interact with political polarization over democratic principles on both sides of the political spectrum. Specifically, we examined how two forms of epistemic relativism—epistemic subjectivism and sociopolitical constructivism—relate to partisan polarization between Republicans and Democrats, democratic values, and policy attitudes. Beliefs reflecting higher epistemic relativism were associated with lower support for democracy and trust in electoral results. Moreover, we identified two subgroups on each side of the political divide (17% of the total sample for Democrats and 16.5% for Republicans) who held a highly politicized conception of truth and a greater willingness to support violations of democratic norms and political violence against their respective out-parties. These subgroups of Democrats and Republicans exhibited many similarities with each other while differing from their own co-partisans. Results are discussed in relation to the upsurge of illiberal tendencies across the political spectrum.