If you've spent any time on a California freeway, you've probably seen an increasing number of Tesla cars on the road bearing anti-Musk bumper stickers.

"I bought this before we knew Elon was crazy," reads one. "Eco-friendly, not Elon-friendly," reads another. Some bear Elon Musk's name or image with a bright red slash through them.

Those defensive messages would seem to validate the reasonable expectation that Tesla Chief Executive Musk's foray into partisan politics — specifically, far-right politics — has sapped the appeal among Democrats and liberals for a product that once proclaimed its owners' commitment to the fight against global warming and other progressive policies.

A new study from Yale researchers has put meat on that bone. They found that Musk's partisan behavior has cost Tesla as many as 1.26 million car sales since October 2022. That's when Musk acquired the social media platform Twitter and gave greater access on it to the far right and other extremist voices.

Musk intensified his partisan journey during the run-up to the 2024 presidential campaign, when he heavily funded Donald Trump's reelection campaign, and after Trump's inauguration, when he launched the DOGE service, which strewed chaos throughout the federal government by instituting mass layoffs purportedly in the name of budget-cutting.

What the sales numbers say is that "it's probably not a good idea to alienate your core constituency with extracurricular political activities if you're a CEO," says Kenneth T. Gillingham, an economics professor at Yale's School of the Environment and lead author of the paper.

The Yale researchers' analysis of sales figures show that Tesla sales were stronger in Democratic-leaning counties than in Republican counties — until October 2022, when they began to plateau in Democratic areas and then began to fall. Tesla sales rose in Republican areas after that break, but not enough to offset the Democratic decline.

The partisan divide in EV sales has been widely studied. Republican and conservative car buyers have never been a target market for EVs generally, and Teslas particularly.

The Yale study also found that overall EV sales in the U.S. continued to rise after October 2022, benefiting non-Tesla makers of EVs and gas-electric hybrids at virtually a one-to-one rate—those products gained by about 1.26 million sales above what they would have been without the Musk effect.

I asked Tesla to comment on the Yale findings, but haven't received a reply.

The Yale study points to the effects of CEO outspokenness for good or ill, especially when their topics have little or nothing to do with their companies' direct interests. It's one thing to go public with concerns about corporate taxes or tariffs, quite another to divagate into divisive political issues such as global warming or anti-LGBTQ discrimination.

The researchers also point to the Musk effect's implications for public ecological initiatives, notably California's EV policies. California's official target is for 25% of new vehicle sales be for zero emission vehicles next, and 100% by 2035. But ZEV sales have stalled out, according to recent figures.

"The 2026 target was set when Tesla was rapidly increasing its sales," Gillingham told me. "Without the Musk effect, it would have been easily met. Now it looks unlikely."

In part that's because buyers who formerly would have opted for a Tesla have shifted to other brands, but are choosing hybrids, which don't meet the EV sales standard, rather than full electric models.

The study comes just as Tesla shareholders are scheduled to vote on a pay package for Musk with an estimated value of $1 trillion. The vote will come at the company's annual meeting Thursday.

As I reported, that pay package treats Musk as the sole indispensable figure in Tesla's future. But although the Tesla board members who approved the pay proposal described the milestones Musk must meet to collect the full value, the standards have been tweaked to make them more achievable than they appear on the surface.

Whether Tesla shareholders will ever come to see Musk as a drag on the company rather than its savior isn't currently clear, but with Tesla stock trading at a meme-level price-earnings multiple of about 320 and a market value of more than $1.5 trillion, that epiphany plainly hasn't occurred yet.

The effect that CEOs' political excursions have on their companies' fortunes has been debated for years. The common conclusion is that it depends on whether their statements and positions align with those of their core customer base, or flout them — whether they will "bolster brand loyalty or trigger a backlash against the CEO's company, as Aaron K. Chatterji of Duke and Michael Toffel of Harvard wrote in 2016.

Chatterji and Toffel examined the impact of several CEOs' criticisms of Indiana's Religious Freedom Restoration Act of 2015, which expanded the ability of defendants in civil lawsuits, including those alleging discrimination, to cite their religious beliefs as justification for their actions.

Among the law's public critics was Apple CEO Tim Cook. Chatterji and Toffel found that Cook's statement that the law might foster anti-LGBTQ discrimination reduced public acceptance of the law significantly, and even increased the popularity of Apple products. Other corporate leaders have spoken out in favor of international initiatives to fight global warming.

Such forthright commentary about current events and issues are rare, however. The reason may be that it's difficult for a high-profile executive to keep track of the shifting winds of public discourse; what may appear to be a popular position at one time can draw brickbats as public opinion evolves. Corporate interests may also outweigh the desire to be heard on issues of public concern.

In recent years, many corporate leaders pledged to stand firm against right-wing assaults on voting rights, access to women's reproductive healthcare, diversity and democracy itself.

Many companies initially promised to end or review their campaign contributions to the 147 Republican lawmakers who voted against certifying Joe Biden's 2020 election victory over Trump. Over time, as it happened, many resumed their contributions.

Toyota, for instance, continued to contribute to some of those politicians, explaining that it "supports candidates based on their position on issues that are important to the auto industry and the company ... We do not believe it is appropriate to judge members of Congress back on their votes on the electoral certification."

How CEO comments are received by their presumed audience can depend on their context. Salesforce CEO Mark Benioff was long regarded as an echt San Francisco liberal billionaire. But last month he came out in favor of deploying the National Guard to patrol the city's streets, evidently aligning himself with Trump's militarization of local law enforcement.

Clearly, Benioff didn't read the room. His statement caused a furor, prompting some entertainment figures to drop out of Salesforce's annual tech conference, Dreamforce, causing the prominent venture investor Ron Conway to resign from a Salesforce philanthropic board, and culminating in Benioff's apologetically withdrawing his suggestion.

Musk is a unique personage in the CEO ranks, as the Yale researchers observe — "the world's wealthiest person and CEO of the most valuable automaker by market capitalization."

Tesla's sales pattern is also unusual in terms of the EV market. The company's unit sales in the U.S. fell year-to-year in 2024 (by 5.5%) and through the third quarter of this year (by 4.3%). In both periods, overall EV sales in the U.S. rose, by 7.3% last year and 11.7% through the third quarter this year.

Tesla has faced a raft of challenges not directly related to Musk's personal behavior: an aging product lineup, competitive models from Hyundai, Audi, GM and Ford, and the Edsel-esque sales flop of Musk's pet project, the Cybertruck.

The Yale researchers took pains to distinguish those factors from the Musk effect by matching auto registrations to county-level Democratic and Republican votes. They found that "more Democratic counties show an increasing propensity to purchase Teslas over time prior to October 2022." After that point, the trend reversed.

By the first quarter of this year, they found, without the Musk effect, Tesla monthly sales would have been about 150% higher than it was. From October 2022 through the first quarter, they calculated, the lost sales totaled 1 million to 1.26 million vehicles, or 67% to 83% of actual sales during the period.

Over the same time frame, sales of EVs and hybrids by Tesla's rivals gained 17% to 22% due to consumers rejecting Musk, providing "a clear example of very significant adverse impacts on corporate performance due to the social and political decisions by one of the world's best-known CEOs."

The Yale paper suggests that Musk may be too well-known to be good for Tesla. His identification with the company has long been crucial for its success and for its high-flying stock price. The new study suggests that Musk has turned, at long last, into a negative.

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