The upper house election is less important than the Liberal Democrats' election win in December 2012, which returned the party to power after a rare hiatus of three years, because the lower house can pass normal bills without the upper house's approval. However, the upper house win solidifies the party's comeback. Under Abe, the party has woven a narrative of national revitalization that centers on economic policies. First came a fiscal stimulus package, and next, bolder-than-usual monetary stimulus after a leadership change at the central bank.

Now the current fiscal and monetary policy combination, which has succeeded in lifting Japanese growth prospects a bit, will continue for the foreseeable future. Of course these are relatively familiar tools that Japanese governments have used to stabilize the economy over the past two decades of deflationary tendencies, if somewhat more aggressively wielded. With the upper house under his control, Abe will unveil the third and most difficult element of his revitalization plan, an attempt to overhaul rules and regulations to increase competition in labor markets, the power sector, foreign trade and elsewhere.

The Liberal Democrats' control of both houses also raises the prospect of a renewed effort to alter the constitution. The party's goal would be to rewrite Article 96 to make constitutional revisions easier, requiring a simple majority in both houses (which the Liberal Democrats now have) rather than a two-thirds majority in both houses and a national referendum. Then the party could tackle the thorny revision of Article 9, which forbids Japan from developing and using military power for purposes other than self-defense. Rewriting the U.S.-written, post-World War II constitution to pave the way for total military normalization would be highly symbolic. It would also be politically difficult. Opinion polls show that the public would prefer that the government focus on boosting growth rather than embroiling the society in a polarizing debate over the constitution. Yet much of the public does not have a strong opinion on the issue, and the government can now claim it has a strong mandate, and may be able to sway the undecided voters with a show of resolve and patriotism. 

Military normalization began in the 1950s, has accelerated rapidly since the rise of China and the driving forces remain in place. Constitutional revision — should it indeed take place in the coming years — would remove many legal obstacles and help shift the domestic perception of what constitutes a legitimate military role, especially regarding military industrial development and collective defense. This step would clearly be consequential. Nevertheless, Tokyo has already shown itself capable of using de facto justifications to take the precautions it deems necessary for national security.

The significance of the upper house election lies primarily in the fact that the ruling party now has considerable political capital and does not face elections in either house until 2016. A bicameral majority and relatively strong public support rarely coincide in Japan. The combination of economic stimulus and U.S. economic recovery could further boost the government's advantage in pushing its agenda. Moreover, this relative political unity comes at a time when China has become weighed down with the social challenges of slower growth, and the rest of the region has shifted to balancing China and thus increasingly sees Japan's security role in a better light than in the past. Tokyo still must work within constraints, ranging from a shrinking population to high indebtedness to its complicated relations with the United States, but it is unlikely to miss this rare window of opportunity.