December 2013 marked the 20th anniversary of the North American Free Trade Agreement (NAFTA), which transformed the United States, Canada and Mexico into a single market largely free of tariffs and other obstacles to the sale of goods from one country to the other. Former President Bill Clinton predicted the pact would create 200,000 jobs. Texas billionaire Ross Perot warned it would lead to a “giant sucking sound” as U.S. jobs flowed into Mexico. Twenty years later, what do you think: Did NAFTA help or hurt U.S. manufacturers?