It has become fashionable to talk of the US-Japan relationship as a relic of a bygone era. President Barack Obama must use his first state visit to Japan today to reassure his hosts of its continued relevance.

His trip comes at a tense moment. China is stepping up its sovereign claims in the Japanese-controlled Senkaku Islands and with its neighbours in the South China Sea. Japan, the Philippines and others worry that the Obama administration is lukewarm in upholding US treaty commitments to them. China, on the other hand, fears the US is trying to contain it.

At a time when the US and its allies are struggling to roll back Russia’s predatory designs on Ukraine, Asia will be reading Mr Obama’s signals very closely. Reassuring America’s allies without stoking Chinese fears will require all his diplomatic skills.