The GOP convinced people that removing regulations and cutting taxes will make US companies more "competitive," globally. I assume that was interpreted as bringing back jobs.
Of course that won't compete with countries willing to pollute their land, sea and air for a buck, has no worker protections, and/or heavily subsidizes it's industry.
Both parties are for open trade, which has the downside of extremely cheap labor for US companies at the expense of domestic labor. US companies send materials to foreign countries, where they are assembled for nearly nothing, under bad conditions, and don't have to worry about industrial waste. The assembled product is then shipped it back to the US, or to it's ultimate desination.
Also, something that isn't talked about much anymore is what was called the "Walmartization" of America. Before Walmart, small towns were fairly autonomous. They had their locally or regionally owned hardware stores, clothing stores, grocery stores, banks, etc. Whenever a Walmart was built (and this applies to most conglomerate companies like banks and farming), it leveraged it's logistics might and shut everyone else out of business. Local politicians didn't do anything about it, probably because they were corrupt, incompetent, powerless or all three. State and federal politicians didn't do anything about it either. Coupled with globalization, these once healthy towns shriveled to nothing. Your options mostly became limited to working at Walmart, working at a fast food joint, or be a public servant.
http://www.nytimes.com/2003/11/15/opinion/the-wal-martizatio...
All this affected the vast majority of land mass in the entire US. Think about that. What other country sits by and lets that happen?
If you can logically analyze (meaning take emotion out of it) the related issues Trump was campaigning on, it was to renegotiate trade deals to improve the US job market and prevent illegal immigration to improve the US job market. Of course both of these were politicized by the establishment (who both love free trade). And of course he didn't do himself any favors, but I think that was the main draw in middle America. Having a honest job with honest pay is so important to a lot of people (for obvious reasons), that everything else that comes with Trump is secondary or ignorable. It's been bad for middle America for decades, starting in the 70s and has gotten worse (and ignored by the parties). Trump is the result of 50 years of not merely frustration but absolute despiration. Remember, not only did he beat the Democratic candidate, he handily beat all of the 20 or so establishment GOP candidates. I think if any other candidate campaigned on the same jobs platform as Trump (regardless of party), Trump would never have gotten elected. Trump is a symptom of the above economic problem, and people offering the same solutions will be elected again.
Here's the Gore/Perot debate on NAFTA in 1992. I'm not convinced open trade isn't just another form of corporate giveaway at the expense of domestic workers.