U.S. farmers, who helped carry Trump to his surprise 2016 election win, have been among the hardest hit as China has imposed tariffs on imports of U.S. agricultural products including soybeans, pork and grain sorghum in response to U.S. tariffs on Chinese goods. Now, increasing frustrations over the prolonged dispute are prompting some rural residents in Iowa, home of the first presidential nominating contest in February, to consider candidates other than President Donald Trump in the 2020 election.