If showing up is half the battle, the Obama administration will do well in China. At next week's annual US-China summit, there will be a total of 15 cabinet secretaries or agency heads in Beijing in an impressive display of diplomatic force.

With so much to discuss, neither government wants the agenda to be hijacked by a ritualistic argument about the level of the Chinese currency. Yet the delicate compromise they have established over exchange rates is at risk of breaking down.

Only a few weeks ago, the issue seemed to have been deftly resolved. Tim Geithner delayed the publication of the Treasury department's annual report on whether China is manipulating its currency and Hu Jintao, president, travelled to the US for an international summit about nuclear weapons, a sign that tensions were easing.