A great many people all along the process.
To benefit from free trade you must first understand the Law of Comparative Advantage, and produce goods and trade goods accordingly.
I'm pretty familiar with Law of Comparative Advantage, but there is lot more to the problem than what's in the economic textbooks.
If Florida can produce the best and cheapest Oranges and Mexico can produce the best and cheapest tomatoes then the absence of trade barriers will allow the Florida orange growers and the Mexican Tomato growers to market their product world wide providing the best products to consumers. So with free trade, industries in each country can produce what they produce best. Consumers get better products, producers can make more money, and government collects more taxes. Everybody prospers. Well, not quite.
Each country must adjust which the US has not been able to do. The Florida tomatoes pickers must get jobs picking oranges of something else. Well, that's not a great deal of adjustment but the same can not be said for other industries. For example, when the TV manufacturing in 80's and 90's moved overseas, workers moved to other electronic manufacturing but slowly almost every electronic manufacturer in the country moved their operations abroad. So these workers were told they must retrain and find jobs in other similar industries but those industries were doing just what the electronics manufactures were doing. So the workers were told they should get college degrees, become healthcare professionals, engineers, and scientist.
The problem of course is that retraining cost big bucks and many, particular older workers didn't have either the funds or the education to pursue such a course. This story is repeated over and over from textiles, to auto parts, to chemical manufacturing.
The bottom line is that free trade has been a disaster for millions of middle income workers, wonderful for consumers, and a bonanza for Wall Street and investors.
Whoever thought US workers would prosper in a free trade environment were nuts. America workers can not compete against labor in countries that pay a dollar an hour for labor with no benefits and little regulations. Americans were sold a bill of goods. We were told the ingenuity, education, and technology in foreign nations would never match the US. American jobs were safe That has certainly proved to be false.
The answer lies not in free trade but rather smarter trade treaties, huge investments in education, infrastructure, and technology. In many countries, government pumps large sums in the building of plants, research, and development giving their industries huge advantages over US industries. The US government has done little to prevent the illegal actives of China and other nations in dumping products on the US market to drive out completion and manipulations in currency market. In other words, we got to be smarter in dealing with these nations which is pretty hard when 40% of the largest US corporations are foreign owned.