Rank-and-file Democrats and independents are considerably more likely than Republicans to take a rosy view of foreign trade, and have been for several years, according to Gallup polling data.
This in tension with the impression you would get from reading articles about the congressional politics of Trade Promotion Authority, where the vast majority of opposition is coming from Democrats, with Republicans singing the virtues of free trade.
Part of the issue here is that Gallup is asking, in general, whether foreign trade is more of an opportunity for the US or more of a threat. The congressional debate is about a specific economic agreement, some of whose provisions are only loosely related to trade.
Another possible explanation is that trade is currently identified in the public's eye with Barack Obama, who has been heavily promoting the Trans-Pacific Partnership. But the timing on this doesn't quite work out — enthusiasm for trade among self-identified Republicans has been in a long-term decline since the early days of the Bush administration. It's perhaps related in some more generic sense to conservatives' greater nationalism.