: will US alliance relationships be weakened as part of the retreat to isolationism espoused by Trump? Or will those alliances be reconfigured to reflect the shifting geopolitical landscape?

Trump has repeatedly emphasised that the US–Japan security relationship is ‘not a fair deal’ because the United States is obliged to defend Japan while Japan is not obligated to defend US territory. Trump has stated that he believes Japan should pay the ‘full cost’ for US military troops stationed in Japan, has threatened a US withdrawal if Japan refuses, and has suggested that it would ‘not be so bad’ if Japan were to develop nuclear weapons. These statements ignore how and why the US–Japan security relationship developed, and belittle the hard work the two countries have invested in strengthening the relationship. Ultimately, such a stance will hurt the United States and its political and economic interests in Asia.

After World War II, the new Japanese Constitution included the Article 9 ‘peace clause’ to prevent Japan from backsliding into imperial militarism. Japan is prohibited from using force to settle international disputes. Therefore, the use of force by Japan to defend United States territory would be considered unconstitutional.

At the same time, forward deployment has been a fundamental element of postwar US security strategy. Establishing US military bases and stationing troops in Europe and Asia during peacetime has allowed the United States to conduct joint drills and training with allies and has acted as an important deterrent to potential conflicts. Assuming that the United States wishes to remain a global leader, forward deployment carries much lower costs as a security strategy than basing troops at home.

A balance of rights and obligations between the United States and Japan has been maintained under the alliance whereby the United States guarantees Japan’s security in exchange for the use of the latter’s land, sea and air facilities for the maintenance of international peace and security in the region. The ability of the United States to utilise military bases in Japan is indispensable to the US forward deployment strategy and to its status as a Pacific power.

The idea that Japan should pay all of the costs for US bases on its territory does not stand up to scrutiny. US military bases in Japan are not merely for the defence of Japan; rather, they serve a broader regional and global purpose within US security policy. The US Navy’s Seventh Fleet, for instance, which has an operational mandate covering the Western Pacific and Indian Oceans, has its home port at the Yokosuka Naval Base in Japan’s Kanagawa Prefecture. From there, it supports American operations in the South China Sea, Afghanistan, and Iraq — all of which are intended primarily to further US interests. Abandoning such a strategy would not benefit anybody in the region, let alone the United States.

Despite its constitutional constraints, Japan has gradually taken on a greater responsibility for advancing shared Japanese and US interests in Asia. Beginning in 1978, Japan rapidly increased its host-nation support for US bases. Under the most recent agreement, signed in December 2015, Japan will pay ¥190 billion (US$1.67 billion) per year in direct costs for US bases over the next five years in addition to hundreds of billions of yen more in related costs to support the US presence. Japan’s level of host-nation support is overwhelmingly more generous than that of any other US ally.

Japan has also been increasing its contributions to US efforts to promote regional stability. For instance, the US–Japan Defense Cooperation Guidelines were revised in 1997, expanding the provision of Japan Self-Defense Forces (SDF) rear-area support to the US military, and again in April 2015, paving the way for the September 2015 security-related bills and recognition of the SDF’s exercise of limited forms of collective self-defence. These changes were all warmly welcomed by the United States as supporting the US-Japan alliance.

Moving out from under the US nuclear umbrella and developing an indigenous nuclear capability is at present unthinkable for Japan. The Japanese development of nuclear weapons would destroy the Nuclear Non-Proliferation Treaty regime and elicit international condemnation. The domestic political costs in Japan would be tremendous as well, given the legacy of the atomic bombings of Hiroshima and Nagasaki. The withdrawal of the US nuclear umbrella would be a deal breaker for the US–Japan alliance. In no way would this be in the national interest of the United States.

Even if Trump ultimately fails to win the US presidency, the rhetoric of his campaign has already put US–Japan relations at risk.

The question of the US role in the world will be a critical issue for the incoming administration. Trump’s rhetoric fails to recognise the interconnected nature of shared global challenges and pushes public opinion toward blind isolationism. A 5 May opinion poll by Pew Research Center indicates that 57 per cent of Americans would rather the United States ‘deal with its own problems, while letting other countries get along as best they can.’ A much greater number of respondents (41 per cent) said that the United States ‘does too much’ to solve global problems rather than ‘too little’ (27 per cent). A tilt toward isolationism will undermine alliance relations, US economic and political interests, and overall regional stability.

Trump’s rhetoric risks undermining confidence in the US security guarantee to Japan. The fact that the presumptive candidate of one of the two major US parties has openly suggested abandoning the alliance is forcing Japanese policymakers to start more actively contemplating previously unthinkable scenarios in case the United States were to actually walk away. This risks setting in motion an evolution in thinking on both sides that is ultimately harmful to US interests.

What, then, must the United States and Japan do in order to continue strengthening alliance cooperation? For one, they should be bolstering cooperation with mutual partners in the region such as South Korea, Australia, India and the ASEAN nations. Japan should also continue to explore options to reduce the US burden, including further expanding the contributions of the SDF, helping to make US military troops stationed in Japan as compact as possible, and instituting joint drills, training and base-sharing arrangements. At the same time, the question of reducing Okinawa’s burden — including how to move forward on the issue of the relocation of US Marine Corps Air Station Futenma — needs to be addressed.

The danger of isolationist foreign policy must be firmly resisted. The US–Japan alliance has played a critical role in securing shared peace and prosperity in Asia Pacific. Throwing away more than 70 years of an alliance that continues to benefit both nations and the region would be a tragic mistake.

Hitoshi Tanaka is a senior fellow at the Japan Center for International Exchange and chairman of the Institute for International Strategy at the Japan Research Institute, Ltd. He previously served as Japan’s deputy minister for foreign affairs.

This article is an extract from East Asia Insights Vol. 11 No. 2 July 2016, which is available in full here, and is reprinted with the kind permission of JCIE.