Japan's postwar edifice has rested on two mighty pillars. The first is its military alliance with the US, its erstwhile conqueror, under whose nuclear umbrella Japan has sheltered since 1945. The second is the Liberal Democratic party, stalwart defender of that alliance, whose benign conservatism supported Japan's extraordinary economic rise. The first of these pillars, the LDP, is about to crumble. What will happen to the other one?

The question is worth asking even though the alliance is made of stronger stuff than a mere political party, however enduring. In a dangerous region still echoing with wartime rancour and groaning under the strain of shifting economic and military fortunes, it will be in the interest of both countries to hold their postwar clinch for years, if not decades, to come.

But the nature of that clinch could change. The centre-left Democratic party of Japan, a loose alliance of LDP defectors, technocrats and former socialists now almost certain to win power next month, has explicitly questioned some of the alliance's sacred cows. In its 2007 manifesto, its latest word on the subject, it said it would “re-examine the role of the US military in the security of the Asia Pacific region and the significance of US bases in Japan”. The manifesto also stressed the importance of building trust with Asian neighbours, particularly China.