Open this photo in gallery: Billionaire Elon Musk was at the Oval Office for a press conference with U.S. President Donald Trump last week. The two have been locked in a feud over Mr. Trump's big budget bill.Nathan Howard/Reuters To an elite class of titanic ruptures that includes Esau and Jacob, Katie Holmes and Tom Cruise, Kim Kardashian and Kanye West, Leonard Cohen and Suzanne Elrod, Shoppers Drug Mart and RBC and, of course, the Beatles, relationship students can add a new one for the ages. This week’s blustery breakup of Donald Trump and Elon Musk is not a split...