U.S. Trade Representative Robert E. Lighthizer, center, Canadian Foreign Minister Chrystia Freeland, left, and Mexican Secretary of Economy Ildefonso Guajardo Villarreal hold a news conference after the fourth round of negotiations for a new North American Free Trade Agreement (NAFTA) on Oct. 17, 2017. (ANDREW CABALLERO-REYNOLDS/AFP/Getty Images)

The next round of NAFTA negotiations begins Friday in Mexico City. The last round ended with harsh words and little, if any, progress on key issues. The standoff between American, Canadian and Mexican negotiators stems from what the U.S. Chamber of Commerce has called “poison pill proposals” from the United States, which Canada and Mexico are unlikely to accept.

As the United States returns to the negotiating table, it’s important to note a surprising post-election trend. Among Trump voters, support for trade has risen dramatically since the 2016 election. This striking surge calls into question just how committed rank-and-file Republicans are to a more protectionist future.

This increasing support for trade is quite a turnaround from the 2016 campaign. In the months leading up to the election, Republicans became much more skeptical about trade — likely echoing Trump’s criticisms about trade agreements.

But that’s changed. In a national probability sample interviewed in October 2016 and again in July 2017, the percentage of Republicans saying that trade helped the U.S. economy surged over 20 points from 2016 to 2017.

Respondents were also asked whether they favored or opposed “the federal government in Washington negotiating more free trade agreements.” Among Trump supporters in October 2016, 20 percent favored more trade agreements and 46 percent opposed them. But by July 2017, 41 percent favored trade agreements and only 17 percent were opposed.

Other surveys show a similar pattern. For example, both Gallup and the Chicago Council on Global Affairs found an increase in support for trade support from 2016 to 2017.

Double-digit shifts in public opinion in less than a year are rare indeed. What’s the cause?

One possibility is that trade support depends on who holds the White House, and Republicans are now confident that trade agreements under Trump will be more to their liking. This is possibly part of the story, but it cannot account for the fact that both Democrats and Republicans have increased in their support for trade since 2016 according to Gallup and the ISCAP Survey. By this theory, Democrats should have less confidence in trade agreements than they did in 2016.

The Republican surge in support for trade also defies expectations about top-down leadership of mass opinion, particularly when it comes to foreign policy. Trump is hardly leading the charge to negotiate “more free trade agreements” as our survey asks, nor is he arguing that trade has helped the U.S. economy. Yet Americans are warming up to precisely this idea.

What about NAFTA itself? A Pew Research Center survey released just this week shows that a majority of Americans (56 percent) believe NAFTA is “good for the U.S.,” and only 33 percent say it is bad. Republicans are much more likely than Democrats to say it has been bad for the U.S., but here the issue is arguably not trade agreements in general but Mexico in particular.

The gap between Republicans and Democrats is widest when it comes to believing that Mexico (but not Canada) is benefiting more than the U.S. This pattern is consistent with the ongoing racialization of attitudes about trade. Despite their disadvantaged economic status, minorities are consistently more pro-trade than whites, and Americans are generally more supportive of trade with light-skinned countries than with dark-skinned ones. This may help explain why Republicans tend to see Mexico, but not Canada, as the stumbling block for NAFTA.

Regardless of the causes of these shifts in opinion, they call into question how much rank-and-file Republicans are committed to a protectionist economic path. Although trade is often bashed by political candidates — including not only Trump but both Mitt Romney and President Barack Obama in 2012 — governing is not campaigning. Obama later supported the TTIP and TPP agreements. Now the American public — including Trump voters — seems to understand that the radical change that Trump is courting is not in their collective interests.

Most elected officials in the United States are well aware that millions of American jobs depend on NAFTA. Reticence about voicing their public support stems from the belief that the American public has turned against free trade. This belief is clearly mistaken.

Diana C. Mutz is the Samuel A. Stouffer Professor of Political Science and Communication at the University of Pennsylvania, the director of the Institute for the Study of Citizens and Politics, and a Non-Resident Fellow at the Chicago Council on Global Affairs.

The 2016-2017 survey was conducted by the National Opinion Research Center at the University of Chicago for the Institute for the Study of Citizens and Politics.