There are a few burning legal questions surrounding the US-China trade talks, which take centre stage again this week as Liu He, the Chinese vice-premier, returns to Washington for a new round of discussions with Mr Lighthizer.

One is whether the Section 301 investigation launched by the Trump administration last year against Chinese unfair trade practices, which provides the legal foundation for the imposition of US tariffs, will be kept open or closed. If it is the former, to the dismay of Beijing, Washington could press ahead at any moment with higher tariffs if it believes China has not complied with the deal (if it happens). That would be more difficult if the 301 probe has been closed.

A second question is whether the deal would be compliant with World Trade Organization rules, and subject to a possible challenge at the Geneva-based body. According to WTO regulations, two countries cannot set preferential tariffs and cut an agreement that excludes others unless it is a fully fledged pact that covers substantially all areas of trade.