Canadian prime minister Mark Carney has strong support at home for his decision to face down the US and collapse a proposed trade deal. Whether this can hold if it turns into a damaging full-scale trade war is unclear. But for now Carney is digging in, with the support of the main opposition party and a strong majority of voters.“America is trying to break us so that they can own us,” he said after the dramatic weekend collapse in the talks, following last minute changes in US demands which Canada could not possible accept. By pushing too far, the US left Carney with no choice but to end the talks.In response, the US president imposed 50 per cent tariffs on a wide range of Canadian imports, ranging from wine, furniture and cement to clothing, fishing rods, hockey equipment and Christmas decorations. This demonstrated both the strength and weakness of Trump’s position – he can target many small and medium sized companies, but Canada also supplies vital imports to the US, for example fertiliser products. And, crucially, the risk for Trump is of a further upward twist to inflation ahead of the mid-term elections in November, as well as a hit to jobs. A trade war would hurt both economies, costing jobs and pushing up prices. Carney said he would impose tariffs in response to Trump’s move, but not until September 8th. This leaves a window to reopen talks. For now, there are no signs of this happening, with Trump now threatening tariffs on Canadian cars from January. However, the US president’s ability to U-turn on trade threats is by now familiar and he faces criticism for his move on Canada not only from the Democrats but from within his own party. The row is just the latest sign of the damage caused by Trump’s wrecking ball trade policy. It will be seen as evidence of the near-impossibility of maintaining balanced trade deals with the US president. If the dispute between Washington and Ottawa persists, it will cost both sides heavily. But in the zero sum world of Donald Trump, the vital thing is to be seen to “win”, whatever the cost.