When the Trump administration more than doubled import fees on Canadian softwood lumber earlier this year, the goal was to support domestic prices and boost US production. Instead, prices have plunged, and mills on both sides of the border are scaling back. A benchmark for the commodity mostly used in construction has plunged 18% since an August peak to the lowest in seven months, driven by sluggish homebuilding activity and a glut of inventory. The drop shows how protectionist measures aren’t always enough to protect domestic industries from broader market dynamics at a time when high interest rates and elevated costs are squeezing consumers and weighing on their confidence, dampening demand for new homes. …“The US producers were looking for more of a price bump from the duties, and they didn’t get one,” said Brooks Mendell, at Forisk Consulting. “The interpretation of that is, well, the demand isn’t there.”