Two neighboring nations bound by decades of economic interdependence now find themselves at the edge of a trade conflict neither may have fully intended. The United States has imposed 50 percent tariffs on $20 billion of Canadian goods, a move that followed the collapse of negotiations each side describes differently — one claiming a deal was abandoned, the other insisting it was never truly within reach. Canada's Prime Minister has pledged to respond in kind, and what began as a negotiation has become a test of political will, with ordinary commerce caught in between.