Canada and the United States have long been cosy trade partners, but that relationship is now tested by US President Trump, who in his first months in office has threatened, paused and reversed tariffs so many times it makes the head spin. …All of this would have been inconceivable 20 years ago, University of BC professor Kristen Hopewell says. And this approach not only will be damaging to the interests of the United States and its major trade partners for years to come, but risks unravelling a system that’s ordered the world economy since the end of the Second World War. It’s more than just topsy-turvy tariffs. Institutions like the World Trade Organization, and its predecessor, the General Agreement on Tariffs and Trade, have defined the rules of trade for nearly a century and helped usher in a period of relative stability and prosperity. And those foundations of trade are now also at stake.