Elon Musk slammed President Donald Trump’s trade adviser Peter Navarro as “truly a moron” and “dumber than a sack of bricks” on Tuesday.

Musk’s insults came in response to Navarro’s comments made Monday on CNBC about Tesla’s manufacturing practices, in which Navarro referred to Musk, Tesla’s CEO, as “not a car manufacturer” but “a car assembler” while arguing that the car company depends heavily on foreign supply chains for items such as batteries.

Now, Musk, who’s overseeing federal spending cuts under President Donald Trump, has fired back at Navarro’s claims.

“Navarro is truly a moron. What he says here is demonstrably false,” Musk wrote on X Tuesday while replying to a social media user who posted a clip of Navarro’s comments. “Tesla has the most American-made cars. Navarro is dumber than a sack of bricks.”

Musk continued: “By any definition whatsoever, Tesla is the most vertically integrated auto manufacturer in America with the highest percentage of US content. Navarro should ask the fake expert he invented, Ron Vara.”

The jab about “Ron Vara” pertains to a fictional economist cited previously by Navarro in his 2011 book “Death by China.” Navarro claimed that the made-up expert was never “improperly” used as a fact source.

The public spat between Musk and Navarro has taken off as the latter defended Trump’s sweeping tariffs, which set off a global stock market fiasco and concern among consumers and politicians as other countries have threatened to wage a trade war with the United States.

Despite the blowback, Navarro, the senior counselor for trade and manufacturing to Trump, argued that the tariffs will help rebuild America’s manufacturing efforts and prevent sourcing from overseas.

“When it comes to tariffs and trade, we all understand in the White House and the American people understand that Elon is a car manufacturer. But he’s not a car manufacturer, he’s a car assembler in many cases,” Navarro told CNBC.

He continued, “If you go to his Texas plant, a good part of the engines that he gets, which in the EV case is the batteries, come from Japan and come from China. The electronics come from Taiwan…”

Navarro added: “What we want, and the difference is in our thinking and Elon’s on this, is that we want the tires made in Akron, we want the transmissions made in Indianapolis, we want the engines made in Flint and Saginaw. And we want the cars manufactured here.”

White House press secretary Karoline Leavitt reacted to Musk’s post  on Tuesday.

“Whatever. We are the most transparent administration in history, expressing our disagreements in public,” she said, according to CNBC senior Washington correspondent Eamon Javers.

Elsewhere while speaking to CNN’s Alayna Treene, Leavitt said that “boys will be boys!” regarding the nasty feud between Musk and Navarro.

“Look, these are obviously two individuals who have very different views on trade, and on tariffs,” Leavitt said. “Boys will be boys! And we will let their public sparring continue.”