by Congress seems likely. It takes only a majority in each House to pass. Democrats alone can't stop it.
Who benefits? Corporations who can sell American goods with no tariffs or other restrictions to the countries of Central America. That includes companies that market genetically modified grain.
Who suffers? Farmers in Central American countries fear the American competition in growing and selling corn and other grains will put them out of business. Workers can expect to be victimized by American corporations who set up factories in Central America to take advantage of local wage rates and laws (or lack of such) that regulate working conditions.
What can we do? I can't do much. I live in a deep blue State. However, I will write Senators Boxer and Feinstein and Representatives Waxman and Sherman to urge them to derail the thing.