Open this photo in gallery: Canadians, reacting to U.S. President Donald Trump’s taunts about Canada becoming the 51st state, are particularly angry with Elon Musk. Trump and Musk speak to reporters as they sit in a Tesla vehicle on the South Lawn of the White House on March 11.The Associated Press Gus Carlson is a U.S.-based columnist for The Globe and Mail. Like so many businesspeople before him, Tesla TSLA-Q CEO Elon Musk is learning that politics is a fickle mistress. In Mr. Musk’s case, it has also become a violent one. In the past few weeks, his company’s vehicles...