Months after he endorsed President Donald Trump, Elon Musk is teasing an “America Party” to challenge Republican and Democratic politicians.

Tesla’s stock price has plunged in response to Elon Musk’s announcement of a new political party and his latest attacks on President Donald Trump. Investors are once again concerned about Musk’s focus as the company’s CEO announced over the weekend that he has launched the America Party.

Mr. Musk’s involvement in politics and his financial support for the president’s campaign was once seen by investors as a benefit to Tesla, fueling a steep rise in company shares after the election last year. That association has now turned into a liability. Tesla shares are down 40 percent from their peak in December.