Sales of Tesla Inc.’s high-end Model S sedan have taken a big hit in the company’s most important U.S. market, California, as the electric auto maker is leaning more heavily on selling the lower-priced Model 3 compact car, new data show.

Falling sales of the Model S—and its sister sport-utility vehicle Model X—threaten Tesla’s growth goals and profit ambitions as it must rely more on its cheaper Model 3 to make up the difference.

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