It all feels rather familiar. Several years of fixing the renminbi to the dollar has brought Beijing under sustained fire from Washington for undervaluing its currency. Senators and congressmen are threatening to hit China with punitive tariffs. It's 2005 all over again.

Back then the threats came to nothing, not least because China allowed the renminbi to crawl higher. But this time they look more serious. In particular, the precision with which retaliation against China is being prepared suggests more willingness to unsheathe the sabre rather than just rattle it.

So what has changed? One obvious answer is the occupancy of the White House and Capitol Hill. In 2005, the administration of George W. Bush set its face against actions such as currency tariffs, and Republican control of Congress made it less likely. Barack Obama, president, in contrast, has signalled more scepticism towards trade and more urgency to act to reduce subsidised imports, agreeing last year to emergency tariffs on Chinese tyres using a measure repeatedly rejected by Mr Bush.