When Japan's prime minister visited Washington this month, Japanese officials lobbied intensely to get him a one-on-one with Barack Obama. In the end, Yukio Hatoyama had to settle for just 10 minutes, and even that during a banquet when the US president was presumably more interested in the appetisers and wine. These things matter in Japan. One senior politician called the put-down – as it was inevitably viewed in Tokyo – “humiliating”. He even noted that the Japanese prime minister was shunted to the edge of a group photo, the diplomatic equivalent of banishment to Siberia.

It would be wrong to read too much into these titbits of protocol (though it is always fun trying). But behind the snub lies something real. The US-Japan alliance, the cornerstone of security in east Asia since 1945, has not looked so rocky in years.

There is a proximate cause. Mr Hatoyama's new government has annoyed Washington by reopening negotiations over the relocation of a marine base on the Japanese island of Okinawa. But beyond the immediate is a nagging suspicion that something bigger is afoot. That is the possibility – remote, but real – that the base squabble is an early warning of a strategic realignment as Japan grapples with the fact of China's rise and an erosion of US influence in east Asia.