Selling a free-trade agreement at home is hard work, given public scepticism about their effect on American jobs. So as supporters of the Trans-Pacific Partnership try to round up backers, they increasingly emphasise the geopolitical case for concluding a deal.

They are correct that a good trade and investment agreement would be geopolitically beneficial, and that a collapse in the talks would be deeply damaging. But too often they overstate the case — and, in doing so, generate real geopolitical risks of their own, while also jeopardising the agreement they seek.

The geopolitical case for TPP is straightforward. It could help US allies in Asia, most notably Japan, reform and thus strengthen their economies, making them more capable geopolitical partners. Asian participants could diversify their economic relationships, becoming less dependent on an unpredictable China. A deal that genuinely offers China the option of eventually joining could also help draw Beijing in a more liberal direction.