Elon Musk, unhappy with Donald Trump’s tariffs, unloaded Tuesday against one of the president’s most visible senior aides on the economic policy, using a slur and calling the official “dumber than a sack of bricks.”

Musk took to his X social media platform to launch the attacks against Peter Navarro, the Trump administration director of trade and manufacturing policy who called the billionaire Tesla CEO a “car assembler” instead of a “car manufacturer.”

Musk used the r-word in one of his tweets on Navarro.

“When it comes to tariffs and trade, we all understand in the White House — and the American people understand — that Elon’s a car manufacturer. But he’s not a car manufacturer — He’s a car assembler,” Navarro, who is also serves as an assistant to the president, said during a CNBC appearance Tuesday.

Navarro said Tesla components are sources from around the world, including batteries from Japan and China and other electronics from Taiwan.

“Tesla has the most American-made cars,” Musk posted Tuesday morning to X, tagging Navarro’s X account. “Navarro is dumber than a sack of bricks.”

In a response to that post, Musk referred to Navarro using a slur for a developmentally disabled person:

Over the weekend, Musk said he hoped trade would eventually be conducted between the United States and Europe without tariffs.

“At the end of the day, I hope it’s agreed that both Europe and the United States should move ideally, in my view, to a zero-tariff situation, effectively creating a free-trade zone between Europe and North America,” Musk said in a video-link interview with Matteo Salvini, Italy’s deputy prime minister and the leader of the far-right League party, during a League congress in Florence, CNN reported.

Under the Trump tariffs announced last week, goods imported from dozens of countries and territories are now going to be taxed at sharply higher rates, and that is expected to drive up the costs of everything from cars to clothes to computers.

These tariffs – which can run as high as 50% — are meant to punish countries for trade barriers that Trump says unfairly limit U.S. exports and cause it to run huge trade deficits.

The Associated Press contributed reporting.