Musk, who had been a close ally of the president, announced on X Saturday that he would be forming the “America Party.” His decision was based on an X poll that he posted on July 4, where he asked users on the social media website if there should be an 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.

Elon Musk said over the weekend he was starting a new “America Party.” That’s “exactly the opposite direction” that Tesla shareholders want, an analyst says.