The misquoted refrain of John Maynard Keynes — “when the facts change, I change my mind” — is often wielded by ministers to explain controversial U‑turns. It’s an ode to their adaptability, a signal of their enlightenment in the face of new data.

Does it reflect how decisions are really made? Hardly. Every day, we see examples that contradict the self-delusion. Despite the costs of HS2 spiralling from £54 billion to more than £120 billion (in 2023 prices), few MPs had shifted from supporting to opposing the project until this week’s ruckus. The falling “bang for the buck” of the railway line seemed detached from one’s thoughts over whether it should go ahead.

A monumental international policy shift is under way that similarly defies evolving evidence. Key figures from both major US political parties, including the president, now repudiate the “Washington consensus”.

This set of prescriptions, encompassing the rule of law, fiscal discipline and market liberalisation, was championed by international institutions and DC in the early 1990s as a blueprint for developing economies to improve their growth prospects.

This shift is, in part, a result of both Democrats and Republicans distancing themselves from the core tenets of the Washington consensus domestically. National conservatives and progressives, including President Biden’s administration, now say that free trade deals enriched corporations at the expense of workers, that China’s accession to the World Trade Organisation hollowed out industrial communities, that industrial policy can create a manufacturing renaissance, and that reshoring production will enhance American economic resilience.

Strikingly, this paradigm shift is occurring just as research is showing the old consensus in a pretty good light. Bill Easterly, a development economist, was a longstanding critic of Washington DC’s top-down penchant for telling other countries what to do. He agreed with critics that these strategies didn’t live up to their promise. Then, in 2019, he reassessed the evidence. His research found far fewer episodes of macroeconomic disasters such as high inflation or big black-market premiums on exchange rates after the policies were adopted.

Plus, he noticed that countries following these guidelines saw their economies grow faster, including in Latin America and Africa. Other experts have backed this up, finding that countries embracing sustained reform towards more economic freedom saw 16 per cent higher GDP per person after ten years compared with others. So the idea that this approach was bad for developing countries? Already out of date.

What about the middle classes here in the West? Last week Larry Summers, the former US treasury secretary, gave a tour de force at the Peterson Institute criticising the shifting thinking. An obsessive focus on Chinese imports causing American job losses, he said, had obscured the American jobs created through more exports, lower input costs and Chinese capital inflows. All things considered, the academic evidence showed that the US benefited substantially from China’s global integration.

Yes, recent years may have underscored the importance of diversifying supply lines rather than being exposed to Chinese monopoly bottlenecks. However, the “new Washington consensus” is not limited to enhancing free trade with non-Chinese allies. It promises that trade and industrial policy will bring back manufacturing to America, a supposed silver bullet for reducing domestic regional inequalities and helping the country decarbonise at the same time.

This thinking, Summers says, is muddled. American unemployment is still around its lowest levels since the 1970s. Inflation has been the big problem squeezing household finances. To be seriously talking of aiming trade policy to boost employment at the cost of higher prices is downright perverse.

Proponents of the “new consensus” remain besotted with the idea of creating manufacturing jobs. They are hopeful, given that Biden’s semiconductor and green energy subsidies have seen a surge in manufacturing construction. Summers warns them not to expect a resultant manufacturing jobs boom. The uptick in investment remains minor on a macroeconomic scale, he says. And, historically, as manufacturing becomes more productive, it requires less labour, just as the demand for manufactured goods stays relatively fixed as incomes rise. A new march of the makers remains a pipe dream.

We see this around the world. The share of total employment in manufacturing has declined precipitously (albeit to different levels) across all advanced economies, irrespective of their trade policies or whether they were running trade deficits or surpluses. Protectionism and domestic procurement provisions cannot guarantee manufacturing jobs. What they do ensure is a less efficient economy that will make it more expensive to decarbonise.

Turning their backs on free trade and trying something different might be more understandable if the US was languishing behind. Overall, though, America is not just remarkably rich, but its GDP per capita is currently surging ahead of European countries, including the more manufacturing-centric Germany.

Why should we care about this US pivot? Well, for the UK it’s not just about our part in reducing global poverty. The US trade discourse is starting to echo in Westminster. Rachel Reeves, the shadow chancellor, cheered on the end of the “old Washington consensus” recently. Labour has pledged to adopt a green industrial policy, “prioritise jobs” in trade deals and implement “buy British” provisions that will make procurement unnecessarily expensive.

Given our more desperate economic plight, there’s a risk of the government reaching for headline-grabbing announcements too. Within conservative circles, there’s growing calls for a beefed-up industrial policy, animated for some by the need to keep up with the US and EU, and for others by the sincere belief it will enhance productivity.

Where such strong convictions stem from is puzzling, given the state of economic knowledge. So, in Keynes’s spirit I’ve been asking advocates: what evidence would lead you to think these policies were misguided? What would change your mind? As yet, I can’t report a good answer.