The American public, already skeptical of free trade, is becoming increasingly hostile to it.

In the latest Wall Street Journal/NBC News poll, more than half of those surveyed, 53%, said free-trade agreements have hurt the U.S. That is up from 46% three years ago and 32% in 1999. Even Americans most likely to be winners from trade—upper-income, well-educated professionals, whose jobs are less likely to go overseas and whose industries are often buoyed by demand from international markets—are increasingly skeptical.

"The important change is that very well-educated and upper-income people compared to five to 10 years ago have shifted their opinion and are now expressing significant concern about the notion of…free trade," said Bill McInturff, a Republican pollster who helps conduct the Journal survey. Among those earning $75,000 or more, 50% now say free-trade pacts have hurt the U.S., up from 24% who said the same in 1999.