Donald Trump tore into an official of the U.S. Chamber of Commerce who accused the president Monday of “weaponizing” tariffs and hurting American businesses, farmers and consumers. Trump responded by insulting Myron Brilliant, head of international affairs at the largest business lobbying organization in the U.S., calling him “not so brilliant.” Trump also accused the association of being more supportive of companies than “for our country” because it did not back his trade war. Brilliant’s attack — and the president’s slam back — occurred on CNBC, with Trump calling into the “Squawk Box” program after Brilliant’s comments.

Brilliant agreed that some international trade agreements need to be renegotiated, but he warned that threats, unpredictability and tariffs aren’t good strategies. “The weaponization of tariffs — the increase of threats on our economy, on our farmers, our manufacturers, our consumers — is going to hurt our country,” Brilliant said. Trump’s trade war last year cost U.S companies and consumers an estimated $3 billion a month in higher prices. The “weaponization” criticism likely referred to Trump’s threat to impose new tariffs on Mexico not because of any trade issue but as a cudgel to force the country to stem the number of immigrants heading to the U.S. border. Brilliant also said that unpredictable change “creates uncertainty with our trading partners.” Trump’s tariff threat just months after negotiating a new trade pact with Mexico sends a message that U.S. agreements can’t be counted on. “The world is watching,” Brilliant warned. A miffed Trump called in later to insult Brilliant and question the association’s patriotism for not supporting his tariffs. The businessman turned president also threatened to “rethink” his membership in the Chamber of Commerce. He again called tariffs a “beautiful thing if you’re the world’s piggy bank.” He didn’t refer to Mexico but said that China will make a trade agreement with the U.S. “because they’re going to have to make a deal.”