“An educated consumer,” the New York haberdasher Sy Syms used to boast in his television commercials, “is our best customer.” The same is not true of trade pacts. Since the passage of the North American Free Trade Agreement 20 years ago, voters have come to understand them better and like them less. True, 54 per cent of Americans see trade as an “opportunity for growth”, according to a recent Gallup poll. But 38 per cent see it as a “threat to the economy”, and they are dug in. Many blame globalisation for the 60,000 plants closed, by some estimates, and the 5m manufacturing jobs lost since Nafta was passed. The White House – negotiating the Transatlantic Trade and Investment Partnership with the EU and the Trans-Pacific Partnership with 12 nations – finds itself failing on both fronts.

Nafta was oversold 20 years ago. It has generated much economic activity but many of its specific promises proved false. It did not stabilise the US trade balance; instead it led to sizeable trade deficits. It did not produce a Mexican prosperity widespread enough to hold down migration to the US; instead it weakened the rural Mexican economy and drove immigration higher. Other trade deals have brought unpleasant surprises, too. Since a pact with South Korea came into force in 2012, US exports there have fallen and the bilateral trade deficit is up more than 50 per cent. Barack Obama’s trade negotiators boast that their “21st century” agreements will avoid some of Nafta’s economic pitfalls. The problem is that the criticism of those agreements is 21st century as well.

Today’s trade deals are more about setting standards and ground rules than about removing tariffs and quotas – which, except for food and clothing, are already quite low in the US. The new pacts get under the skin of the those who distrust global capitalism, just as the old pacts did. But they also provoke unwonted unease among market libertarians. Thus, Lori Wallach of the anti-Nafta group Public Citizen was one of the heroes of the 1999 Seattle street protests against the World Trade Organisation, but her sophisticated, left-leaning arguments against granting “fast-track” authority to today’s US trade negotiators might also convince the constitutional literalists who inhabit the various Tea Party groups.