Former Vice President Kamala Harris took a swipe at her onetime boss, Joe Biden, calling his 2021 decision to exclude Elon Musk from a White House electric vehicle event a “big mistake” — comments that came as the 82-year-old former president undergoes radiation therapy for prostate cancer.

Harris, who appeared Tuesday at Fortune’s Most Powerful Women Summit in Washington, D.C., said she believed the snub — which was widely seen as a political favor to organized labor — was mishandled and had lasting repercussions.

“I write in the book that I thought it was a big mistake to not invite Elon Musk when we did a big EV event,” Harris told Fortune Editor-in-Chief Alyson Shontell.

Former Vice President Kamala Harris took a swipe at her onetime boss, Joe Biden. Getty Images for Fortune Media

“I mean, here he is, the major American manufacturer of extraordinary innovation in this space,” Harris said of Musk.

The former vice president has made numerous public appearances in recent weeks to promote the release of her memoir, “107 Days,” in which she criticized Biden for his “recklessness” in running for re-election despite his declining health.

In August 2021, Biden hosted executives from General Motors, Ford and Chrysler parent Stellantis to promote a goal of making half of all new vehicles sold by 2030 zero-emissions — but Tesla, the country’s top EV maker, wasn’t invited.

At the time, then–White House press secretary Jen Psaki said the event featured “the three largest employers of the United Auto Workers,” pointedly noting that Tesla’s workforce isn’t unionized.

Reporters pressed her on whether the lack of an invite was punishment for that.

Psaki replied: “I’ll let you draw your own conclusion.”

Harris told Fortune Editor-in-Chief Alyson Shontell on Tuesday that it was a “big mistake” not to invite Elon Musk to an EV event at the White House in August 2021. Getty Images for Fortune Media

Musk, whose company sells more EVs than all three companies combined, tweeted then: “Yeah, seems odd that Tesla wasn’t invited.”

A month later, he called the Biden administration “not the friendliest” and said it seemed “controlled by unions.”

Biden’s White House at the time defended its outreach to Detroit’s Big Three, calling them key partners in the president’s push for union jobs.

Musk, meanwhile, accused the administration of bias, mocking Biden on social media after SpaceX’s first all-civilian mission went unacknowledged by the president.

During Tuesday’s Fortune event, Harris said presidents should “put aside political loyalties” when recognizing technological achievement.

Elon Musk is CEO of Tesla, which sells the most electric vehicles of any company in the US. REUTERS

“So, I thought that was a mistake, and I don’t know Elon Musk, but I have to assume that that was something that hit him hard and had an impact on his perspective,” she said.

The former vice president’s remarks echoed a passage from her new book in which she writes that the Biden administration’s decision alienated Musk, who later emerged as one of President Donald Trump’s top financial backers.

Musk contributed nearly $300 million to GOP-aligned groups during the 2024 election cycle.

Harris also used the Fortune stage to say the Biden administration’s early legislative priorities were misplaced.

“When we made the decision as an administration to put the infrastructure bill and the CHIPS Act first, I actually think that was a mistake,” she said.

The Biden administration declined to invite Tesla and Musk due to pressure from unions, according to reports. AFP via Getty Images

“Very important work, no question, but we did that before putting the immediate needs ahead of anything else.”

Harris said the White House should have moved faster on child care and paid family leave, warning that voters felt abandoned as inflation soared.

“If we can’t meet the basic needs of the people, there will be this backlash, which is going to resonate and sound like it is about ‘blame the rich’,” she said.

“It’s about, ‘we need help for our basic needs, and please prioritize those needs’.”

According to reports at the time, Tesla officials repeatedly sought meetings with the White House after the inauguration but were rebuffed amid pressure from the United Auto Workers.

Then-President Joe Biden is seen behind the wheel of a gray Jeep Wrangler Rubicon electric vehicle on the South Lawn of the White House in August 2021. Bloomberg via Getty Images

When Musk learned Tesla wouldn’t be invited, officials called the company with an apology, according to the Wall Street Journal.

Weeks later, Biden credited GM’s Mary Barra with having “electrified the entire automobile industry” — a line that infuriated Musk, whose company had already delivered more than 115,000 EVs in the US that quarter compared with GM’s 26,000.

Biden’s aides later tried to mend relations, arranging calls between Musk and top White House officials, according to the Journal. But the tension lingered.

Musk increasingly aligned himself with Republicans, railing against “the woke mind virus” and denouncing Democratic policy priorities. By 2024, he was bankrolling Trump’s comeback bid through a super PAC called America PAC.

The former vice president’s comments mark her sharpest public criticism yet of the administration she helped lead — and they come as Biden faces his most serious health battle since leaving office.

The snub was one of the key factors that motivated Musk to back President Donald Trump, according to reports. REUTERS

On Saturday, Biden was photographed leaving evening Mass at St. Joseph on the Brandywine Church in Wilmington, Del., his first public appearance since beginning a five-week course of radiation and hormone therapy for Stage 4 prostate cancer.

Aides say the treatment is ongoing and described his cancer as “high-grade” but hormone-sensitive.

Photos showed a frail-looking Biden walking slowly and holding onto a woman for support. The scar above his right eye from recent skin cancer surgery remained visible as he greeted parishioners.

The Post has sought comment from Biden and Musk.