IIt's loneliness At the top. So lonely, in fact, that sometimes U.S. presidents and titans of industry have only one person of equal stature: each other. For nearly two centuries they've played golf together, enjoyed movie nights and told each other jokes. Some have developed genuine friendships; others have openly hated each other. Of course, it's an unequal relationship. Although chief executives tend to stay on longer than presidents, there's no doubt who's higher in the hierarchy. But rarely has a mogul's dealings with past, present and possibly future presidents been as difficult as Elon MuskWho once enjoyed Barack Obama's generosity and is now his cheerleader-in-chief Donald Trump,