Elon Musk’s spat with President Trump’s trade advisor, Peter Navarro, is breaking out into an all-out war, with the world’s richest man calling the fellow senior staffer “a moron” on Tuesday. Mr. Musk has been subtly criticizing Mr. Trump’s new tariffs for days, criticism that Mr. Navarro says is rooted in the Tesla owner’s own greed. 

On Tuesday morning, an X user with whom Mr. Musk regularly interacts shared a clip of Mr. Navarro saying that Teslas are mostly made with materials from overseas, materials that are now subject to the president’s tariffs. 

“The American people understand that Elon’s a car manufacturer. But he’s not a car manufacturer — he’s a car assembler, in many cases,” Mr. Navarro told CNBC. “The batteries come from Japan and come from China. The electronics come from Taiwan.”

“Navarro is truly a moron. What he says here is demonstrably false,” Mr. Musk wrote in response.

In another post, Mr. Musk said Mr. Navarro was “dumber than a sack of bricks.” He also tagged an account called @IFindRetards, and referred to the White House advisor as “Peter Retarrdo.”

Mr. Musk went even further, bringing up allegations that the Harvard-trained economist invented a fake expert named “Ron Vara,” a name that happens to be an anagram of Mr. Navarro’s surname, to justify some of his more contentious trade arguments in the salons of Washington.

“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,” Mr. Musk said. 

When asked about the public war between the two presidential advisors on Tuesday, White House press secretary Karoline Leavitt simply said, “Boys will be boys.”

“These are obviously two individuals who have very different views on trade and on tariffs,” Ms. Leavitt said. “We will let their public sparring continue, and you guys should all be very grateful that we have the most transparent administration in history.”

The world’s richest man — who has taken a multi-billion dollar haircut following recent declines in the share price of his Tesla stock — has been gently saying for days that he hopes tariffs will ease, especially between America and Europe, where Mr. Musk sells about half of all his Teslas. 

In response to Mr. Musk’s criticisms of the tariffs, Mr. Navarro pointed out in an interview with Fox News that the Tesla chief is simply looking out for his bottom line. 

“We just have to understand: Elon sells cars,” Mr. Navarro said on Sunday. “He’s simply protecting his own interests, as any businessperson would do.”

“We’re more concerned about Detroit building Cadillacs with American engines, and that’s what this is all about,” Mr. Navarro added.