ALL this week, crowds have been waiting in hushed lines to view a yellowing document on display at the National Archives in Tokyo. For many, Japan’s war-renouncing constitution, written by an occupying army during a few sweltering days in 1946, is something of a sacred text. But Japan’s prime minister, Shinzo Abe, has made little secret of his desire to amend it. He chose the 70th anniversary of its entry into force, on May 3rd, to announce that he would try to secure changes to it by 2020, when Tokyo hosts the Olympics. That will require the approval of both houses of the Diet, along with popular assent through a referendum. The inevitably contentious debate will consume a huge amount of political energy over the next three years, possibly at the expense of Mr Abe’s already flagging economic reforms.

Mr Abe wants to end questions about the legality and appropriate use of Japan’s not-quite army, the Self-Defence Forces (SDF), by amending Article 9, the constitution’s iconic pacifist clause. This prohibits Japan from maintaining land, sea or air forces, which sits a little awkwardly with the SDF’s 250,000-odd servicemen, 1,600 aircraft and a fleet boasting four large helicopter-carriers. It also leads to endless debates about whether it is legitimate for Japan to participate in international peacekeeping missions, for example.

Many in Mr Abe’s Liberal Democratic Party (LDP) have long viewed Article 9 as a humiliation, imposed by the victorious Americans. After all, says Keiji Furuya, a politician, the party was born in 1955 with the explicit aim of amending the constitution. Mr Abe’s grandfather, Nobusuke Kishi, tried hard to revise it while he was prime minister in the 1950s. (He failed.)

Mr Abe has started his campaign on a forceful note. “Those members of the public who think of the constitution as an immortal tome are now a small minority,” he told his supporters. He has some reason to be confident: his ruling coalition has a hefty parliamentary majority and, with the help of like-minded parties, commands two-thirds of both houses—the required strength needed to call a referendum. North Korea’s frequent missile tests are helping to make his case for him.

Yet there is ample room for miscalculation. A new poll by NHK, Japan’s state broadcaster, finds that just 25% of the public want Article 9 rewritten, with 57% opposed. Support for constitutional change peaked over a decade ago; young people, in particular, have grown wary of foreign entanglements, says Eiji Oguma, a sociologist. Mr Abe himself concedes that the economy is a bigger concern for most voters. By pursuing unfinished family business too eagerly, he may end up delaying its completion yet again.