A growing experimental literature suggests that international law appears to have a larger impact on public opinion than constitutional law. Because the former U.S. policy of separating migrant families at the border arguably runs afoul of both the Constitution and international law, it provides an unusual opportunity to explore the normative pull of these norms experimentally in a single context. We fielded survey experiments with national samples in July 2018 and November 2020, asking respondents how much they supported the policy. We find that telling people that the policy is unconstitutional increases support for the policy, but only when the issue was receiving heavy media coverage, and that international law has no comparable effect on public opinion. We attempt to explain these seemingly counter-intuitive results in two ways. First, in studies that explore the impact of constitutional law, respondents may be “unsuccessfully treated.” Second, constitutional law treatments can trigger a backlash effect through defensive processing of information on constitutionality.

Kevin Cope & Charles Crabtree, Migrant-Family Separation and the Diverging Normative Force of Higher-Order Laws, 51 Journal of Legal Studies, 403–426 (2022).