Final answer:
Bill Clinton secured the reduction of protectionist tariffs by supporting the ratification of the North American Free Trade Agreement (NAFTA), which was ratified by Congress in late 1993.
Step-by-step explanation:
Bill Clinton achieved his goal of reducing protectionist tariffs primarily by supporting ratification of the North American Free Trade Agreement (NAFTA). NAFTA, initially negotiated by the Bush administration, was designed to eliminate tariffs and trade restrictions among the United States, Canada, and Mexico. Clinton helped allay concerns arising from NAFTA's potential impact on American jobs and the environment by adding side agreements to protect workers and the environment, respectively. Through these efforts, the treaty was ratified by Congress in late 1993, leading to the creation of one of the world's largest common markets.