Generally agree with your comment. Read Ricardo for backup.
Everyone benefits from “free trade” - the sellers and they buyers.
Raising tariffs protects inefficient industries and raises the price of goods. More people in the economy are hurt when tariffs go up than are hurt with low tariffs that can displace some workers in select industries.
The problem is that trade is often not “free” and is not always fair. Dumping occurs when a country sells product for less than it cost to make it. Dumping is a serious problem that disrupts supply chains, domestic industries and displaces workers. Trade deals are supposed to protect domestic economies from dumping practices but need to be aggressively enforced.
Trump is only partly correct in his view on US trade deals. The US has negotiated good trade deals because our tariff structures are comparatively low, and we get more tariff reduction for our exports to other countries than other countries get in tariff reductions for their exports to the US. Historically (up to and including NAFTA) the US has made some good deals, and then aggressively beats countries over the head when they fail to comply. Trump’s criticism of US trade policy may be more valid when focused on the crony capitalism that Obama ascribes to. The scope of TPP, for example, goes beyond “trade” into other areas of the economy, so the value of TPP is suspect. We all know Obama does not favor deals that enhance or strengthen the US position in the world economy. Since Obama is apparently motivated to knock the US down a few notches, Trump’s criticism of current US policy has validity.