Democrats are growing frustrated with the richest man in the world, Elon Musk, and his influence over President Trump. Desperate to wound the South African-born mogul, some are charging that — as a naturalized American citizen — he isn’t loyal to the Stars and Stripes.

“Mr. Musk has just been here 22 years,” the Democrat of Ohio, Congresswoman Marcy Kaptur, said at the Capitol on Wednesday, as if citizenship has a probationary period. This gave voice to the xenophobic impulse that, in our nation of immigrants, is best confined to the shadows.

Noting that Mr. Musk is “a citizen of three countries,” Ms. Kaptur asked, “When push comes to shove, which country is his loyalty to? South Africa, Canada, or the United States?” She then repeated for emphasis. “And he’s only been a citizen, I’ll say again, 22 years.”

On Thursday, the host of ABC’s “The View,” Joy Behar, made similar charges. She said Mr. Musk was “not born in this country,” and that he “was born under apartheid in South Africa; so, he has that mentality going on.” She presumed to read his mind.

Ms. Behar alleged that Mr. Musk “was pro-Apartheid.” Yet he left South Africa at 17 in 1988, two years before segregation ended. Investigations have never uncovered evidence that he supported the South African system, only that he fled it.

The fact that Mr. Musk took the oath to become an American carried little weight with Ms. Behar. “Yeah,” she said, “he’s a citizen, right? He’s a natural now. He’s a naturalized citizen. Really? How did he do that? Did he come over the border legally?” He did — on a student visa.

Later, Ms. Behar said that she was “getting flack” for saying “that Musk was from apartheid,” as she put it. “I don’t really know for sure if he was … maybe he was, maybe he wasn’t.” This coyness fed the narrative that Mr. Musk ought to be viewed with suspicion because of his birthplace.

These insinuations aside, it’s legal for Americans to hold multiple citizenships. This has been law since the Supreme Court ruled in 1967’s Afroyim v. Rusk that the 14th Amendment’s citizenship clause protected that right.

USA.gov states that individuals holding multiple citizenships “do not have to choose one nationality over the other.” Democrats, of course, are free to object. The argument, though, undercuts their stance of embracing immigrants and their claim to the moral high ground.

The citizenship attacks betray partisans driven to self-destruction by Mr. Musk, who offers many safer angles for criticism. There’s his free-speech absolutism on X. there’s the fact that he’s unelected to any post but is wielding power.

That Mr. Musk used to be a darling of the left makes some MAGA supporters view him with a gimlet eye, too. There’s also his personal life. Others dislike Mr. Musk because his net worth, $357.5 billion, is greater than the gross domestic product of most countries.

Before the xenophobic whispering, all these chinks in the SpaceX founder’s armor — and his performance at the Department of Government Efficiency — had already weakened his public standing.

Last week’s Washington Post-Ipsos poll found that 34 percent of American adults approve of how Mr. Musk is doing his job; 49 percent disapprove.

In November, Politico interviewed several Democratic consultants about why the party didn’t use the “nationalist” angle as a “weapon.” They found a reluctance rooted in the party’s embrace of immigrants and minority groups.

That Democrats didn’t focus on Mr. Musk’s origins was “maybe,” Politico wrote, “to their credit.” Party members “claim to oppose the politics of delegitimization, and people ought to practice what they preach.” Now, some on the left are delivering darker sermons.

Taunting Mr. Musk because he was born elsewhere insults all who have gone through the civic baptism of a naturalization ceremony. America holds that all who raise their hands to swear the oath of loyalty are full and equal citizens — no probationary period required.