Former President Trump clashed with the editor-in-chief of Bloomberg News during an economic forum in Chicago on Tuesday over the GOP nominee’s insistence that tariffs would not have negative consequences in a possible second term.

Bloomberg’s top editor, John Micklethwait, repeatedly pressed Trump at the Economic Club of Chicago over his plans to impose a universal tariff on imports and his threats to use tariffs on American companies that outsource their manufacturing. 

Micklethwait noted Trump’s plans would essentially halt trade with China, place at least a 10 percent tariff on European nations and have a drastic effect on the U.S. economy, where 40 million jobs rely on trade.

“That is going to have a serious effect on the overall economy,” Micklethwait said.

“It’s going to have a massive effect — positive effect. It’s going to be a positive effect,” Trump responded. “It must be hard for you to spend 25 years talking about tariffs as being negative and then have somebody explain to you that you’re totally wrong.”

Micklethwait noted that critics have said Trump’s tariff proposals for all imports would amount to a national sales tax, with $3 trillion worth of imports affected and companies passing on higher costs to buyers.

“That is just simple mathematics, President Trump,” he said.

“It is, but not the way you figured. I was always very good at mathematics,” Trump replied, suggesting higher tariffs would make it more likely for foreign companies to build factories in the United States.

Micklethwait told Trump that perhaps the gravest risk with tariffs would be on foreign policy, essentially hitting allies with economic penalties.

“How does it help you take on China turning all of your allies against you?” he asked.

“Tremendously, because China thinks we’re a stupid country,” Trump said. “They can’t believe somebody finally got wise to them.”

The former president has repeatedly pitched tariffs as something of a blanket solution for lowering costs, even in areas such as child care, as well as for reducing the deficit and encouraging domestic manufacturing.

While Trump has claimed the use of tariffs would lower costs, economists have repeatedly said it would cause companies to pass higher costs onto consumers and could worsen inflation. And experts have disputed Trump’s claim that tariffs would bring in enough for the U.S. government to offset the deficit.

Tuesday’s event marked a rare confrontational interview for Trump, who for the past month has largely spoken only to conservative media.