A poll from agriculture magazine Farm Futures this week showed that only 78 percent of farmers who voted for President Trump in 2016 would still vote for him today.
The magazine surveyed 924 farmers from July 20 to August 2.
The poll zeroed in on trade wars as a key factor in the drop.
Out of the farmers surveyed, 40 percent said that the president's actions on trade have "done permanent damage to agriculture."
But farmers showed strong support in other areas, with 86 percent in favor of the president's drive to reduce regulations and 90 percent supporting White House actions on immigration.
The poll results come as the White House rolls out tariffs on another $16 billion in Chinese imports.
The move prompted Chinese newspapers to warn the U.S. not to swing the "stick of hegemony" against China.
Meanwhile, a separate and broader poll from Morning Consult for CNBC showed that rural support in key agriculture states is rising or staying the same overall.
Approval for Trump among rural voters in Iowa increased despite a dip in the price of soybeans.
From January to May, 48 percent of rural voters approved Trump's job performance overall, and increased to 51 percent in July during the start of the trade war.
In Indiana, 56 percent of rural voters approved of Trump between January and May, with that number increasing to 60 percent in July.
Read More:
Trump's Trade War Becoming A Hot Potato For California House Republicans (San Francisco Chronicle)
Trump's Approval Rating Remains High Among His Rural Base, Even As The Trade War Rages, Poll Shows(CNBC)