The Democratic Party (Minshuto) came in to power on a wave of disgust with the LDP, who had been in power almost uninterruptedly since the war and had become associated with all that was wrong with Japanese politics. Even more than with Obama in the US, their support has pretty much unravelled and disillusionment is rife. Now, thanks to Wikileaks, we know that all that talk of moving American bases off Okinawa and giving the long-suffering inhabitants a break was so much hot air. They had secretly let the Americans know that if they said no, the Japanese were prepared to accept it. Read more here, courtesy of the Asahi:
EDIT: that Asahi article has now been taken down for some reason. Here’s one from the American military site Stars and Stripes:
Report: Japan never fully committed to moving Futenma off Okinawa
asazuke 
I’ve added a new link to a different source for that info. It’s more-or-less the same content as the Asahi had.