“Continental energy security” was the watchword of both governments and industry for much of the past quarter century in North America: the idea that by linking the U.S. and Canada in a tight web of pipelines and refineries, both countries would protect themselves from threats and hostile trade actions that — it was assumed — would come from outside North America.

The website of the Canadian Association of Petroleum Producers is still littered with references to the now-obsolete notion that increasing interdependence with the U.S. would make Canada safer: “Over the past decade, Canada has strengthened its continental energy security by reducing reliance on overseas oil and increasing the share of imports from the United States.”

Too late did Canada realize that the threat would come from inside the house — that Americans would elect a president who saw Canada not as a partner, but as a target for extortion and even annexation.