The Globe and Mail reports in its Friday edition that on Monday, Donald Trump becomes president again. The Globe's Tony Keller writes that blocking energy exports, especially oil, is Canada's most powerful economic weapon. It is our atomic bomb. This weapon, however, if it ever has to be used, will not necessarily restrict its damage to the U.S. economy. Its use could be dangerously radioactive for Confederation. The fallout could take the real but limited economic harm from threatened Trump tariffs and escalate it into an existential threat to the country -- exactly what Mr. Trump is dreaming of when he goes on about Canada becoming his 51st state. Canada is urging Mr. Trump not to launch an economic strike, emphasizing potential painful retaliation. However, Alberta Premier Danielle Smith opposes even threatening the use of oil as leverage. In the sad eventuality that the U.S. hits Canada with tariffs, and we hit back with oil-export controls, Mr. Trump might see advantage in offering Albertans a way out: become the 51st state! (Or maybe a mere territory, such as Puerto Rico.) Exit Canada, escape the tariffs and say goodbye to arguing with the rest of Confederation about building pipelines to the Atlantic or Pacific.