Americans usually punish the incumbent party when they elect a president against a backdrop of rising imports, according to a new study. That could foreshadow bad news for whoever emerges as the Democratic nominee from the presidential contest that got under way in Iowa this week.

Low-wage manufacturing jobs are threatened by import competition, and the fear of losing them tends to drive voters away from the party in power, argues a working paper published by the Cambridge, Massachusetts-based National Bureau of Economic Research. That scenario is in play this year as the strong dollar widens the U.S. trade deficit—although, like everything about the 2016 election, the story may be more complicated this time around.

In both parties, outsider candidates—especially Republican Donald Trump and Bernie Sanders on the Democratic side—are appealing to populist anti-establishment voters, saying they'll stand up for workers who risk losing their jobs because of trade. That message has helped fire up crowds on the campaign, but it's not clear how the enthusiasm will translate to votes; at the first caucus in Iowa on Monday, Senator Ted Cruz won over Trump, while Democrat Hillary Clinton secured a slim margin over Sanders.