Tech billionaire Elon Musk slammed President Trump’s trade advisor Peter Navarro on Tuesday, calling him “truly a moron” in their latest spat over the administration’s new import taxes.

“Navarro is truly a moron. What he says here is demonstrably false,” Musk wrote on X in response to a video of Navarro discussing Tesla’s assembly process for its electric vehicles.

Navarro, in the CNBC interview, claimed Musk’s Tesla is not a “car manufacturer,” but rather a “car assembler,” that puts together parts from other countries.

Tesla, led by Musk, has long touted itself as a leader in U.S. domestic production. The company produces all of its North American vehicles in the U.S. at factories in California and Texas, though some of its parts do not come from the U.S.

Musk pushed back on Navarro’s claims, stating Tesla “has the most American-made cars.”

“Navarro is dumber than a sack of bricks,” he added, writing later, “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.”

Musk also mocked Navarro with a derogatory term for someone with a mental disability.

Trump’s 25 percent auto tariff went into effect April 2 as part of his larger trade war. He has argued the tariffs will encourage foreign car manufacturers to move production into the U.S. and increase American jobs.

Despite Tesla’s focus on U.S. production, the company still took a hit amid the global market rout. The company’s stock fell 19 percent since Trump’s tariff announcement last week.

Tesla previously warned it could be further exposed to retaliatory tariffs should other countries respond to Trump’s tariffs.

Navarro and Musk tangled earlier this week over the Trump administration’s sweeping tariffs, which went into effect last week and roiled the stock market.

“A PhD in Econ from Harvard is a bad thing, not a good thing. Results in the ego/brains1 problem,” Musk wrote in reply to a video of Navarro defending the administration’s reasoning for its latest slate of tariffs. 

Musk reportedly later slammed Trump’s trade adviser, saying, “He ain’t built s‑‑‑.” The post, however, appears to have since been deleted.

Musk, who is leading Trump’s so-called Department of Government Efficiency (DOGE) efforts, has pushed for a “zero-tariff situation” between the U.S. and Europe.

“Both Europe and the United States should move, in my view, to a zero-tariff situation, effectively creating a free trade zone between Europe and North America,” he said during a recent appearance hosted by Italy’s right-wing League party, adding, “That has certainly been my advice to the president.” 

Navarro, a staunch critic of trade deals, responded that Musk “doesn’t understand” during an interview on Fox News’s “Sunday Morning Futures” over the weekend.

“It was interesting to hear Elon Musk at the beginning talk about a zero-tariff zone with Europe. He doesn’t understand that,” he said. “And the thing that’s, I think, important about Elon to understand, he sells cars. That’s what he does.”

Despite the spats, Navarro said he believes Musk is “great” when he is “in his DOGE lane” and pointed to his business interests.

“But we understand what’s going on here,” Navarro continued. “We just have to understand. Elon sells cars, and he’s in Texas assembling cars that have big parts of that car from Mexico, China, the batteries come from Japan or China, the electronics come from Taiwan.” 

“And he’s simply protecting his own interests as any business person would do,” he added. “We’re more concerned about Detroit building Cadillacs with American engines. And that’s what this is all about. So it’s fine, there’s no rift here.”