Elon Musk’s ascension as a top adviser to President-elect Donald Trump gives him tremendous power to sculpt the new administration’s approach to electric vehicles — and is sparking renewed scrutiny of his motives. Trump’s announcement that the Tesla CEO would join the pharmaceutical entrepreneur Vivek Ramaswamy in running a so-called Department of Government Efficiency not only offers Musk an opportunity to sway Trump on federal policies that affect all automakers. It could also...