THE protesters mounting an all-night vigil outside Camp Schwab, an American military base on the main island of the southern prefecture of Okinawa, are hardly wild-eyed radicals. Former civil servants, schoolteachers and professors are among those attempting to block trucks bringing supplies for the construction of a vast new facility in and near the camp, to be used by American marines. Riot police have been trying to disperse them. Some of those attempting to reach the base by canoe have been stopped by coast-guard vessels and re-launched in rough waters. But opponents of the planned base are backed by Okinawa’s new governor, Takeshi Onaga, a conservative politician formerly of the ruling Liberal Democratic Party (LDP). Mr Onaga won a landslide election victory last November with a pledge to stop the project. That conservatives are standing alongside left-wingers in opposition to the base could spell trouble for the Americans. Okinawa hosts about half of all 53,000 American troops in Japan; their 32 military sites occupy nearly a fifth of the main island’s tiny area. That outsized burden has long rankled Okinawan residents. The Americans do not want to lose even more public support for their presence, which they and Japan consider vital to regional security.

In 1996 American officials agreed to relocate the most unpopular base, at Futenma. Ten years later a site at Henoko, adjacent to Camp Schwab (see map), was formally selected. Henoko is sparsely populated, in contrast to Futenma. But the new base would ruin a coral-filled bay. Hiroshi Ashitomi, a protest leader, says that according to ancient Okinawan lore a paradise known as nirai kanai lies out to sea.

In December 2013 the Japanese prime minister, Shinzo Abe, broke the impasse by persuading Mr Onaga’s predecessor, Hirokazu Nakaima, to reverse the opposition that had made him popular, and agree to start landfill work. Mr Onaga, however, is sticking to his guns. On February 6th he launched a review of Mr Nakaima’s decision, with a view to overturning it. One question will be how a study commissioned by Mr Nakaima could have concluded that the planned base would have little effect on the dugong, an endangered sea-cow that grazes off the coast at Henoko.

The central government has made clear its irritation with Mr Onaga. Mr Abe and other senior LDP figures have refused to meet him. In January the government cut by 5% Okinawa’s yearly subsidy, the source of nearly half of its budget.

Both American officials and anti-base activists note that Mr Onaga may already be softening his stance. One member of his review panel worries that the governor may have appointed too many conservative lawyers to it who are not especially worried about the Henoko project. By the time the panel releases its verdict this summer, construction may have proceeded so far that even Mr Onaga would balk at the cost of stopping it and having to compensate the central government for doing so.

There are few other obvious options for relocating it, however. No mainland prefecture would willingly accept a new base and its rowdy marines. One long-mooted possibility has been to fold Futenma into Kadena, a massive American air-force base on Okinawa. But the Americans do not like the idea. One American officer jokes that the base would be so crowded in the event of conflict that helicopters would have to park on its golf course. For now, despite the bases, anti-American feeling does not run deep on Okinawa. But that could change if residents’ wishes are ignored, says Mr Ashitomi, the protest leader. The demonstrators, he says, could shift to demanding the removal of all American military sites on Okinawa. That could put the Americans, and Mr Abe, in a bigger quandary.