On Tuesday a US-Canada trade dispute intensified as Justin Trudeau and Donald Trump clashed over softwood lumber and dairy tariffs. This dispute is just one of the trade confrontations the Trump administration has already faced in its short term and could be a major indicator of how Trump and his team handle negotiations going forward.

The lumber and milk fall-out sets the two sides up for a wider battle as they renegotiate the North American Free Trade Agreement. In the grand scheme of things, milk and lumber aren’t particularly important for each side. Last year Canada exported $5.7 billion (nominal) in...

