Existing political economy models explain the politics of trade policy using inter-industry differences. However, this article finds that much of the variation in U.S. applied tariff rates in fact arises within industry. I offer a theory of trade liberalization that explains how product differentiation in economic markets leads to firm-level lobbying in political markets. High levels of product differentiation eliminates the collective action problem faced by exporting firms while import-competing firms need not fear product substitution. To test this argument, I construct a new dataset on lobbying by all publicly traded manufacturing firms from reports filed under the Lobbying Disclosure Act of 1995. I find that productive exporting firms are more likely to lobby to reduce tariffs, especially when their products are sufficiently differentiated. I also find that highly differentiated products have lower tariff rates. The results challenge the common focus on industry-level lobbying for protection.