The sharp increase in suppport for the North American Free Trade Agreement (NAFTA) poses a challenge to many of our conceptions of public opinion. Most large shifts in public opinion follow major events. Based on models estimated from the September to November NBC News/Wall Street Journalsurveys, I show this was not the case with respect to public opinion on NAFTA. Instead, the increase in support for the pact reflected a slower response to a public debate over the merits of free trade versus protectionism. As the debate proceeded, large segments of the public— including the least interested—developed more highly constrained belief systems. By the end of the public discourse, the most and least interested citizens both linked attitudes on the merits of trade to their positions on NAFTA and to their evaluations of the elites on each side of the issue. People made up their minds on NAFTA on the basis of arguments about trade, not about their own self-interest. The NAFTA case suggests that there may be a “rational public” at the individual level after all, even among people who may not usually be interested in public affairs.