July 7–8, 2025: The first trading day since Musk’s weekend announcement, Tesla shares tumbled, and Musk’s personal fortune dropped by as much as $15 billion, according to the Bloomberg Billionaires Index. As of July 9, it stands at $349 billion with Tesla shares broadly unchanged.

Tesla shares sank Monday after CEO Elon Musk announced he would form a new political party in an escalation of his feud with President Donald Trump.

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.