Key Takeaways Tesla shares tumbled after CEO Elon Musk announced that he plans to start a new political party, reigniting concerns that his attention will turn away from running the EV maker and that a public feud with President Trump will escalate.

Mr. Musk’s involvement in politics and his financial support for the president’s campaign were 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.