Ag leaders and farm state lawmakers last week urged farmers and others involved in agriculture to turn up the volume on their support for the North American Free Trade Agreement (NAFTA) amid growing signs that the Trump administration may be ready to dump the 23-year-old trade pact.

“The key thing for us who have benefited from NAFTA is to extol the benefits and as widely as possible right now,” said Philip Seng, head of the U.S. Meat Export Federation (USMEF). “It would be a big mistake if the United States left NAFTA, and it’s even been harmful of us to even threaten to leave it.”

Kansas Sen. Pat Roberts, chairman of the Senate Agriculture Committee, said it is critical for agriculture ...