How do you slash, cut, restructure and even dismantle parts of the federal government? If you’re President-elect Donald J. Trump, you turn to two wealthy entrepreneurs: the spaceship-inventing, electric-car-building owner of a social media platform and a moneymaking former pharmaceutical executive who was once one of your presidential rivals. Mr. Trump said on Tuesday that Elon Musk and Vivek Ramaswamy will lead what he called the Department of Government Efficiency. It will be, he said...