The purpose of this study was to elucidate why some portions of the U.S. public in recent years have become critical of international trade agreements, against their economic interests. To this end, I constructed and tested a hypothesis that a combination of the following two factors has increased opposition to international trade agreements. The first factor is that generalized trust (trust in strangers with different backgrounds) came to have a strong influence on the U.S. public’s trade preferences as the tertiarization of the U.S. economy declined the visibility of economic interests from trade. The second factor is the long-term decline in the generalized trust of the U.S. public as a result of widening inequality. The results of my analysis supported the above hypothesis, except for the part that widening inequality is the main cause of the decline in generalized trust.