After climbing into a Tesla Model S last week, President Trump pledged to buy one. The next day, the Fox News host Sean Hannity said he had bought a Model S Plaid to support the embattled company, saying a Tesla “has more American parts in it than any other car made in our country.” In a backlash to the backlash against the tactics of Elon Musk’s Department of Government Efficiency, prominent conservatives are rallying to the side of the electric car company led by Mr. Musk. They are hoping to swing enough like-minded consumers to offset a boycott of the...