Similarly, a Pew Research Center survey released on Wednesday found that a plurality of Americans making under $30,000 per year say that their family’s finances have been hurt by free trade agreements (44 percent) rather than helped (38 percent). By contrast, those making more than $100,000 per year overwhelmingly believe free trade has been beneficial — 52 percent said trade agreements have helped their family’s finances versus only 29 percent who said they have hurt.

This economic divide on trade has existed for decades. On average, polls conducted from 1981 to 2002 found that support for free trade policies or agreements was 23 percentage points higher for Americans at the 90th percentile of the income distribution than for those at the 10th percentile, according to research conducted by Martin Gilens, a Princeton professor. In his book “Affluence and Influence: Economic Inequality and Political Power in America,” Mr. Gilens concludes that “U.S. policy on tariffs and trade during the past few decades has clearly been more consistent with the preferences of the affluent and has become more so over time as trade barriers have fallen and bipartisan support for an open trade regime has strengthened.”

One indication of the strength of elite support for free trade is the way that even Democratic presidents who enjoy strong support from labor unions have promoted free trade pacts. Bill Clinton passed the North American Free Trade Agreement against majority opposition from within his party during a time when Democrats controlled both houses of Congress. While President Obama no longer has Democratic majorities in Congress, he similarly chose to advance trade promotion authority through the Senate largely with the support of Republicans — only 14 members of his party backed him Friday.