Tesla shares plunged nearly 7 percent on Monday as investors registered dismay at Mr. Musk’s plans to form a third party and his intensifying feud with President Trump.

Yaccarino announced her departure from the CEO role Wednesday on X, formerly Twitter.

Instead of the quadrennial dream of No Labels, in which high-minded donors put up the money for an imaginary white knight who never materializes, we may get the “America Party,” in which the world’s ...