According to a study published in the Journal of International Economics, NAFTA reduced U.S. manufacturing pollution: “On average, nearly two-thirds of U.S. manufacturing reductions in coarse particulate matter (PM10) and sulphur dioxide (SO2) between 1994 and 1998 can be attributed to trade liberalization to NAFTA.”  Maquiladoras (Mexican assembly plants that absorb imported components and produce goods for export) have become the emblem of trade in Mexico. They left the United States for Mexico, hence the debate about the loss of American jobs. Revenues in the maquiladora sector had increased by 15.5% since nafta in 1994.  Other sectors have also benefited from the free trade agreement and the share of non-cross-border exports to the United States has increased over the past five years [when?], while the share of exports from border states has declined. This has led to rapid growth in non-cross-border metropolitan areas such as Toluca, Leén and Puebla, all more populated than Tijuana, Ciudad Juérez and Reynosa. National procedures for ratifying the agreement in the United States are governed by the legislation of the Trade Promotion Authority, which is also known as the fast-track authority. The OBJECTIVE of NAFTA was to remove barriers to trade and investment between the United States, Canada and Mexico. The implementation of NAFTA on January 1, 1994 resulted in the immediate removal of tariffs on more than half of Mexican exports to the United States and more than one-third of U.S. exports to Mexico. Within 10 years of the implementation of the agreement, all U.S.-Mexico tariffs should be eliminated, with the exception of some U.S. agricultural exports to Mexico, which are expected to expire within 15 years.
 Most of the trade between the United States and Canada was already duty-free. NAFTA also aimed to remove non-tariff barriers and protect intellectual property rights on marketed products. On November 30, 2018, the USMCA was signed as planned by the three parties at the G20 summit in Buenos Aires.   Disputes over labour rights, steel and aluminum prevented ratification of this version of the agreement.   Canadian Deputy Prime Minister Chrystia Freeland, U.S. Trade Representative Robert Lightizer, and Mexican Under-Secretary of State for North America Jesus Seade officially signed a revised agreement on December 10, 2019, ratified by the three countries on March 13, 2020. USMCA countries must comply with IMF standards to avoid exchange rate manipulation. The agreement requires disclosure of market interventions.
The IMF may be summoned as an arbitrator if the parties argue.  After the election of President Trump in 2016, support for NAFTA was highly polarized between Republicans and Democrats. Donald Trump has expressed a negative view of NAFTA, calling it “the worst trade deal ever adopted in this country.”  Republican support for NAFTA has grown from 43% in 2008 to 34% in 2017.