For all the outrage Donald Trump generates as US president, he’s yet to do anything irredeemably stupid. There is, however, plenty of time left to mess up; one such upcoming test must be the attempted renegotiation of the North Atlantic Free Trade Agreement (Nafta), due to conclude in the first quarter of next year.

Trump’s insistence that free trade must mean fair trade is a reasonable enough aspiration; after more than two decades in operation, it’s also only right that Nafta should be revisited and modernised.

But to describe it, as Trump has, as “the worst trade deal ever” is quite a stretch, and if he goes through with his threat to withdraw, it doesn’t bode well for British hopes of securing a similarly beneficial trade deal.

As it stands, Nafta accounts for approximately a quarter of all world trade, with millions of jobs at stake. It’s been extremely good news for Mexico and Canada; its rewards for the US are more questionable. Lots of jobs have been lost to low-cost Mexican competition, and there are entirely legitimate concerns around some aspects of the deal with Canada.

Since it came into operation, moreover, the US’s trade deficit with both Mexico and Canada has ballooned. This does not mean, however, that the US has had no benefit whatsoever, as Trump seems to believe. US supply chains and businesses have become deeply vested in Nafta. Were it to collapse, the impact on Mexico would be much greater than on the US and Canada, but all three economies would experience higher costs and consumers a big rise in prices.