Comparing the estimated gaTT/WTO coefficients with non-reciprocal trade agreements, we find that for both exports from recipient countries to developed countries and exports in the opposite direction, the impact on GATT/WTO is greater than for non-reciprocal agreements, and the difference between estimated coefficients is statistically significant at 1%. Membership of the World Trade Organization (WTO) excludes, to some extent, the creation of reciprocity contracts, since WTO Member States undertake to give all other members treatment of the most favoured nation (extending all trade concessions granted to third countries to Member States). Democrats voted much more in favor of trade liberalization than Republicans, but were not consistent in their preferences. Mp Henry Rainey (D-IL) and members of Roosevelt`s government, Rexford Tugwell, Raymond Moley and Adolf Berle, were skeptical of tariff reductions during the Depression. However, the government decided to use a Democratic-controlled congress and presidency to impose the RTAA. In 1936 and 1940, the Republican Party ran on a platform to lift tariff reductions guaranteed under the RTAA. But when they reclaimed Congress in 1946, they did not act to remove tariffs. In the years since the adoption of the RTAA in 1934, the economies of Europe and East Asia had been decimated by the violence of World War II, which left a huge global production gap filled by American exporters.  During the war, the United States had the highest positive balance in its history. Republican preferences for tariffs began to shift as exporters in the home districts began to benefit from stronger international trade. In the 1950s, there was no statistically significant difference between Republicans and Democrats on customs policy, a change that has lasted ever since.  As more and more U.S. industries began to benefit from tariff reductions, some of them began to campaign with Congress for lower tariffs.
Until RTAA, Congress had been mainly pressured by industries that wanted to create or increase tariffs to protect their industry. This change has also helped to maintain many of the benefits of trade liberalization. In short, the political incentive to increase tariffs has diminished and the political incentive to reduce tariffs has increased.  The next natural step is to divide the fake PTA taking into account the group to which each trading partner belongs (Column 4). The results indicate that preferential trade agreements have a positive impact in all four cases. The most significant effect is trade flows between industrialized countries (0.3984), while point estimates for the other three combinations range from 0.111 to 0.248.