When the far-right activist Tommy Robinson emerged from a London courtroom this week after a judge cleared him of a terrorism charge, he gave thanks to the man he said had bankrolled his defense. “Elon Musk, I’m forever grateful. If you didn’t step in and fund my legal fight I’d probably be in jail,” Robinson said. “Thank you, Elon.” In the period immediately after Musk’s messy departure from the White House, the Tesla CEO repeatedly suggested that he was done with politics. Investors who had pushed him to refocus on his businesses were delighted. Tesla’s stock rose. The months since,...