A fourth round of talks involved a U.S. demand for a sunset clause that would end the deal in five years, unless the three countries agreed to maintain it, a provision said by U.S. Commerce Secretary Wilbur Ross would allow countries to end the deal if it didn`t work. Canadian Prime Minister Justin Trudeau met with the Committee on Ways and Means Houses because Congress is expected to pass laws that roll back the treaty`s provisions if Trump tries to pull out of the pact.  The pact catalyzed Mexico`s transition from one of the world`s most protectionist economies to one of the most trade-open. Mexico had reduced many of its trade barriers in 1986, when it concluded the WTO`s precursor To the General Agreement on Tariffs and Trade (GATT), but still had an average pre-NAFTA tariff level [PDF] of 10%. A study published in the August 2008 issue of the American Journal of Agricultural Economics showed that NAFTA increased U.S. agricultural exports to Mexico and Canada, although most of the increase occurred a decade after its ratification. The study focused on the effects on trade flows of phase-in periods in regional trade agreements, including NAFTA. Most of the increase in members` agricultural trade, which has just been placed under the responsibility of the World Trade Organization, is due to very high trade barriers prior to NAFTA or other regional trade agreements.
 In its May 24, 2017 report, the Congressional Research Service (SIR) wrote that the economic impact of NAFTA on the U.S. economy was modest.