This dissertation examines how trade protection is justified and contested across three levels of contemporary politics: international institutions, domestic interest-group coalitions, and the mass public. Each chapter studies a different currency of justification––scientific evidence, organized coalitions, and political rhetoric––and asks how protectionist measures are sustained or disciplined once that justification is scrutinized. The first chapter asks how the World Trade Organization constrains regulatory protectionism despite the erosion of its adjudicatory enforcement. Analyzing 50,599 Technical Barriers to Trade and Sanitary and Phytosanitary notifications (2010–2024), I show that the WTO operates as an epistemic regime in which governments signal regulatory legitimacy through the volume of justificatory evidence they disclose. Regulatory credibility follows a non-linear pattern: both minimal and excessive evidence invite peer scrutiny and revision, while intermediate disclosure attracts the least. Peer comments, not litigation, drive modification. The second chapter turns to the domestic politics that produce trade-restrictive regulation. Linking 1,788 U.S. regulations notified to the WTO to 1.25 million public comments, I use large-language-model classification to map actor coalitions across rulemaking rounds and estimate their effects on three outcome margins: whether a rule is finalized, how its stringency moves, and how extensively the agency engages comments. Opposition from locally concentrated producers is the most robust veto force; the modal supportive coalition pairs advocacy groups with industry associations; and mass-mobilization campaigns systematically depress finalization. The third chapter examines reactions at the mass level. Across two survey experiments on tariff retaliation, I find that voters reward the rhetoric of toughness but punish the material costs of tariffs once those costs become salient: conservative-styled rhetoric raises support primarily among anti-trade and Republican respondents, yet escalating to costly tariffs mobilizes only a narrow base while alienating moderates, and trade preferences prove elastic, shifting with co-partisan leadership rather than fixed material interest. Together, the chapters trace one argument: contemporary trade protection succeeds or fails not through enforcement or material interest alone, but through the contested evidentiary, coalitional, and rhetorical justifications that surround it.