Following the passage of the North American Free Trade Agreement (NAFTA) in 1993 and the Uruguay Round Agreement in 1994, the United States appeared to be on the verge of an era of unprecedented trade liberalization. Since that time, however, the United States has struggled to pass almost every important trade liberalization bill. Results indicate that the factor most likely responsible for the difficulty in achieving trade liberalization over the last 15 years is shifting pressures within the U.S. House of Representatives related to partisanship and constituency.