There's nothing about CAFTA that's unconstitutional, despite what you may read. Congress ratifying any treaty regarding trade is, in fact, Congress regulating international trade, per Article I, Section 8, Clause 3 of the Constitution. If they don't ratify it, that too is regulating international trade. Whatever action they take is the regulation of international trade.

Ideally, trade agreements are mostly a good thing though. If they're negotiated and enforced properly, they make sure countries like China and Mexico don't have an inherent advantage in the market due to the fact that workers in those countries make next to nothing compared to Americans, thus making their products cheaper and providing incentive for American corporations to outsource jobs.

However the human rights provisions in such agreements are rarely enforced. So you just end up with American companies taking advantage of the cheap international labor to cut U.S. jobs and then more jobs are lost when U.S. companies lose business because they can't compete with the cheaper alternatives.