The ruling Liberal Democratic Party’s (LDP) upper house members are traditionally more independent than their lower house counterparts, which means they could present political challenges for Prime Minster Shinzo Abe’s administration if they are swayed by public opinion, said Corey Wallace, an expert on Japan’s security with Freie Universitat Berlin.

If the upper house refuses to vote and leaves the legislation as it is, the lower house would be forced to pass the bills with a two thirds majority, Wallace said, stirring even greater controversy.

Another likely scenario is for the LDP to seek a compromise with opposition parties and scale back some of the most controversial aspects of the legislation.

“It really depends on how much political capital Abe wants to spend, and how important it is to him to have the legislation passed in the form it is now,” Wallace said.

Japan’s constitution, written by the United States after the second world war, prohibits deployment of troops for “collective self-defence” – allowing it to fight alongside allies. Under the legislation, Japan could deploy troops overseas to defend its allies but only when not doing so would threaten the lives and survivals of the country. Experts said the legislation would enhance US-Japan alliance, giving Tokyo greater freedom to provide logistical support.

Abe has argued that the legislation is necessary in the face of increasing threats in the region, in particular from a stronger Chinese military. But many constitutional experts have said this violates Japan’s post-war constitution. The legislation has also set off large-scale protests.

Amid wariness of being dragged into unnecessary conflicts, policymakers are expected to debate how exactly Japan would want to exercise collective self defence, said Stephen Nagy, an associate professor at International Christian University, Tokyo.

“[Japanese] people still feel unattached to conflicts in other parts of the world, it would be hard for political leaders to garner their support [for overseas troop deployment],” Nagy said.

Known for its advanced weaponry and technologies, Japan’s military is regarded as one of the strongest in the region.

“The big question is whether the Japanese government, its people and even the SDF itself, are psychologically ready for the increased risks to the safety of SDF personnel, and possible combat-related deaths, a danger exacerbated by the passage of these bills,” said Brad Williams, an assistant professor and Japan expert at City University of Hong Kong.

Given widespread opposition and the decline in the administration’s approval ratings, some analysts have already compared Abe’s push for the security bills with his grandfather’s efforts to revise the US-Japan alliance 55 years ago that led to his resignation from the premiership.

But so far, the opposition parties have failed to tap into the growing reservoir of public disenchantment, Williams said.

“The ruling coalition is hoping that public opposition will die down after the bills become law and people will just move on, much like in the aftermath of the highly contentious renewal of the US-Japan Security treaty in 1960,” Williams said.