Donald Trump’s most consequential construction project may not be a ballroom or an arch, but his tariff wall. His latest threat to raise tariffs to 50 percent on some Canadian goods, as drastic as it is, is not nearly as significant as what’s coming next. By the end of this month, the administration is expected to introduce major tariffs on dozens of countries intended to ensure what once was a temporary regime lasts well beyond this presidency. Unlike most previous rounds of tariffs, including the ones just threatened on Canada,…