Outside of Sanders's and Trump's coalitions, however, there is little evidence of a broad reaction against free trade. Americans are deeply conflicted about the issue, as shown in two recent polls that came to opposite conclusions about public opinion on free trade.
One was a Gallup poll published last month, which found that a majority of Americans — 58 percent — see foreign trade as an economic opportunity. Just 33 percent said foreign trade was an economic threat. The share of respondents who are optimistic about trade has increased since the financial crisis. Perhaps as Americans are seeing the country as more economically secure, they've become less worried about competition from abroad.
Seven years ago, at the beginning of 2009, just 44 percent of those polled said that trade presented an opportunity. Among Democrats — who are more optimistic about the state of the economy under President Obama — the number seeing economic opportunity in trade increased even more sharply, from 43 percent in 2009 to 63 percent today. The figure among Republicans shifted from 45 percent to 50 percent.
That finding — overall optimism about trade, with partisan divisions — contrasted with the conclusion of a poll published Thursday by Bloomberg. "Opposition to free trade is a unifying concept even in a deeply divided electorate," the authors wrote.
Some of the Bloomberg poll's more striking findings seem to suggest a deep skepticism of international economic exchange. For example, Americans are overwhelmingly resistant to the idea of foreign ownership of factories on U.S. soil. Sixty-eight percent said they'd prefer a domestically owned factory in their communities to a Chinese-owned plant offering twice as many jobs.
Likewise, nearly two-thirds said that there should be more restrictions on imported goods, and 82 percent said they'd be willing to pay "a little more" for domestically produced goods in order to protect domestic workers from foreign competition.
These contrasting results show that Americans see both sides of the debate over trade. They also suggest that politicians can win over voters by focusing on either the costs or the benefits, Frank Newport, the editor in chief at Gallup, said in an interview.
"Americans are very much looking for guidance" on complex economic issues, he said. "You can shift people one way or the other. They’re open to argument."
For example, Newport noted, the Bloomberg poll asked about restrictions on imports, but not on exports, which would mean fewer opportunities for U.S. workers. Americans even have different feelings about imports depending on the industry. They are comfortable with the idea of imported electronics but want to protect American agriculture, Gallup has found.
A Pew poll last year revealed even more contradictions. Respondents were more likely to say that free trade had helped their families' finances than that free trade had made them worse off. When asked about the economy in general, though, they were more negative. The poll found that Americans were equally divided on the question of whether free trade improved economic growth, and much less likely to say that trade created opportunities for employment than that it reduced wages and put Americans out of work.
Previously, economists had argued that workers displaced because of competition with manufacturers overseas would quickly find work in other sectors. That hasn't happened, wrote economists David Autor, David Dorn and Gordon Hanson in a paper earlier this year. The costs of trade in the labor market have been higher than predicted, and they've been concentrated in particular sectors and regions of the country.
Those consequences for particular groups aren't clearly reflected in the overall polling data. As Newport said, there are some people in both parties who vehemently oppose trade, maybe because they have been affected by globalization themselves. Those are the groups that Trump and Sanders hope will help mobilize their campaigns.
These candidates might be able to win over some voters if they can focus on how competition from imports has negatively affected those workers, Newport said. "Jobs," he added, is "a magic word."
"There are a few words out there that Americans react very strongly to," he said. "They're willing to sanction almost anything to bring in more jobs."