President Trump's trade wars resulted in a net loss of five congressional seats for Republican candidates in the 2018 midterm elections, according to a paper circulated Monday by the National Bureau of Economic Research.

The study found that the trade war dragged down GOP candidates in districts that suffered from its effects but provided no benefit to the party in the districts that economically benefited.

"The negative relationship between retaliatory tariffs and Republican support was concentrated in politically competitive counties where Trump narrowly lost the popular vote in 2016, and in counties hardest hit by retaliatory tariffs on agricultural products, particularly those imposed by China," the report found. The analysis, which has not undergone peer review, estimates that the trade war accounts for 10% of the decline in Republican House candidates’ vote share between 2016 and 2018.

The results were particularly bad for the GOP because Republicans lost ground in the counties where they had gained the most in the prior two election cycles. The study found that the trade war "contributed meaningfully" to the 2018 "Blue Wave," in which Republicans lost a total of 40 House seats.

[Opinion: GOP making big gains in 2019 after 2018 'blue wave']

The study was authored by Dartmouth professors Davin Chor and Emily Blanchard, as well as Chad Bown, a senior fellow at the Peterson Institute for International Economics. "I don’t think we had strong expectations, one way or the other, before we started the study. We had heard lots of anecdotes on both sides. Ultimately, as economists, we just let the data and the research answer the question," Bown told the Washington Examiner.

China has significantly cut back on soybean and other crop purchases from the United States since the start of the trade war, at one point suspending purchases entirely. U.S. exports were $206 billion in September, down about $7 billion, or less than a percent, from last year. The U.S. saw a $1.5 billion decrease in exports of food, feed, and beverages, with soybeans representing the bulk of the decline at $1 billion. Auto and auto parts exports fell by $1 billion.