The Free Trade Agreement established by president Bill Clinton distorted the Markets and killed American business. It allowed China to outperform American made products, turning America into a nation of consumers and not builders. It played a substantial role in the financial crisis that occurred in 2008, and continues to effect the economy in a bad way.
"The effects of current FTAs shed some light on the likely effects of the proposed new agreements. The Congressional Budget Office recently analyzed the effects of NAFTA over its first eight years using a statistical model of U.S.-Mexican trade.(6) That model indicated that by 2001 (eight years into the agreement), NAFTA had increased U.S. exports to Mexico by only 11.3 percent ($10.3 billion, or 0.12 percent of U.S. GDP) and had increased U.S. imports from Mexico by only 7.7 percent ($9.4 billion, or 0.11 percent of U.S. GDP). According to the model, the agreement had almost no effect on the U.S. trade balance with Mexico, and what little effect it did have was positive in most years--a $0.9 billion increase (or 0.01 percent of GDP) in 2001. On the basis of those estimates and the results of other studies in the economics literature, CBO estimated that the expanded U.S.-Mexican trade resulting from NAFTA increased annual U.S. GDP by a small amount-- probably a few billion dollars or less.
Although not perfect, the North American Free Trade Agreement (NAFTA) should be considered a success. One fallout was when American companies moved to Mexico for cheaper labor. However, in terms of trading partners, it makes sense for America to ally itself with Canada and Mexico for a free trade zone. Imports and exports move more freely between the three countries in a natural alliance of border states.
Nafta, and Free Trade Agreements in general (including TPP) are good for businesses, as they provide tax incentives to relocate where labor costs are lower. Workers lose out because the better paying jobs leave. It's a race to the bottom, and workers in the United States are the ones who lose the most.
It has done more harm than good. The cost on the manufacturing sector and the damage that has done to the middle class and economy at large outweighs the benefits of tariff/tax free trading. The financial benefits resulting from NAFTA have mostly gone to the economic elite, anyway, and far more jobs have left the country than have been created.