U.S. President Donald Trump attends a meeting with NATO Secretary-General Jens Stoltenberg | Stephanie Lecocq/EFE via EPA Trump at NATO summit: ‘I am fighting for a level playing field for our farmers’ US president says ‘other countries’ trade barriers and tariffs’ destroy American businesses.

U.S. President Donald Trump on Wednesday sought to soothe the concerns of U.S. farmers, offering a reassurance that he has their interests in mind even as his saber-rattling on international trade has stoked fears of a trade war that could put the U.S. agriculture industry at risk.

“I am in Brussels, but always thinking about our farmers. Soy beans fell 50% from 2012 to my election. Farmers have done poorly for 15 years. Other countries’ trade barriers and tariffs have been destroying their businesses,” a post to the president’s Twitter account read. “I will open things up, better than ever before, but it can’t go too quickly. I am fighting for a level playing field for our farmers, and will win!”

The post appeared as Trump was taking part Wednesday in the NATO summit in Brussels, where he has come face-to-face with many of the same world leaders with whom he clashed over trade at last month’s G7 summit. The U.S. president has long complained that his nation is the victim of unfair trade practices by the EU and has imposed tariffs on it, as well as on Canada and Mexico, in an effort to reset those trade relationships on terms more beneficial to the U.S.

The president’s tweet also appeared minutes after an appearance by Senator Chuck Grassley (R-Iowa) on Fox News’ “Fox & Friends,” where he said both he and his constituents are “very, very nervous” about the president’s trade policies, particularly as they pertain to the agriculture industry, which would be particularly vulnerable in a trade war.

Grassley warned that the president’s tactics have the potential to be “catastrophic” not just for farmers or Iowans, but for the entire U.S. economy. The “uncertainty” wrought by Trump’s threats, Grassley said, has already had a devastating impact.

“We do know this, that if the president, the negotiator is, brings these negotiations to the brink, and if he doesn't go over the brink, we know that it’s going to be better for the United States. But if he does go over the brink, it’s going to be catastrophic,” Grassley said. “And with the price of soybeans and corn falling way it has, it’s already been catastrophic if you want to sell your beans and corns today. If you wait a while, maybe you can do better. Or if you sold them two months ago you do better. But this has had very detrimental impact on current markets.”