The Japan-South Korea relationship is continuing its downward spiral. Both sides appear to be glancing sideways at the United States in the hope and expectation that Washington will step in and help remedy the situation. This circumstance accentuates the importance of the U.S. maintaining unbreakable relationships of trust with each of its two treaty allies, both of whom are critical partners in contending with a resurgent China and a recalcitrant North Korea.

Against this backdrop, the timing seems awkward for questions about the utility of the U.S.-Japan alliance to be arising on the Washington policy circuit.

Former U.S. Senate Majority Leader Mike Mansfield, who served as U.S. ambassador to Japan for an astonishingly long tenure from 1977 to 1989, was famous for describing the U.S.-Japan relationship as “the most important bilateral relationship in the world, bar none.” Former Defense Secretary Dick Cheney said that “the U.S.-Japan partnership has become the cornerstone of American security policy in Asia.” But today discussion continues in Washington about the durability and even the utility of the Japan-U.S. security treaty, as well as basing arrangements for U.S. forces in Japan.

Concern was recently expressed on both sides of the Pacific when the Trump White House reportedly was discussing whether the time had come to terminate, or at least significantly revise, this critical alliance. “Wealthy, wealthy countries that we’re protecting are all under notice,” President Donald Trump succinctly stated earlier this year at the Pentagon. “We cannot be the fools for others.”

Withdrawing U.S. troops from Japan — which former Prime Minister Yasuhiro Nakasone described as “America’s unsinkable aircraft carrier” — would, of course, diminish U.S. response capability in the Indo-Pacific region and beyond. For starters, withdrawing to California the aircraft carrier now forward-deployed with the Seventh Fleet in Yokosuka, Kanagawa Prefecture, would cost about 20 percent in deployment length. More broadly, troop withdrawal would reduce training opportunities and the ability to form relationships with host nation forces that some would describe as the glue of the alliance.

In this context, some critics fail to realize that U.S. troops in Japan are not only responsible for defending Japan; they also play a major regional role. Forward deploying U.S. forces in Japan is a visible, physical indication of U.S. commitment to Asia and greatly enhances U.S. ability to respond nimbly to numerous regional contingencies. The forward presence of U.S. troops in Japan also serves as the “tip of the spear,” which in time of crisis may be bolstered by larger forces that require more time to deploy. As such, U.S. troops in Japan serve as a strong deterrent, if not counterweight, to Chinese expansionism and aggression, as well as North Korean adventurism.

Elements of the U.S. forces in Japan are also well situated to assist with scenarios ranging from regional humanitarian assistance-disaster relief operations, to non-combatant evacuation operations for U.S. citizens and others in times of crisis. Disassembling the U.S. forward engagement posture would mean having to deploy forces from out of theater when they are most needed, which could result in the U.S. being “a day late and a dollar short.”

Nor could around 50,000 U.S. troops precipitously withdrawn from Japan easily be redeployed within theater. For example, the U.S. has long planned to redeploy 4,100 U.S. Marines from Okinawa to Guam; this relatively limited move is proving to be a protracted and expensive process.

A new military facility is being built in northern Guam near Andersen Air Force Base, scheduled for completion in 2026, and will host some 5,000 marines (including the 4,100 from Okinawa) and around 2,400 dependents. Expanding that number would be problematic: Guam already hosts some 7,800 U.S. service members. The U.S. Government Accounting Office has estimated construction costs related to the Guam move at around $8.7 billion, of which Japan will pay about $3.1 billion. Similar challenges exist for plans to move around 2,700 troops from Okinawa to Hawaii.

Should the decision be made rapidly to withdraw U.S. forces from Japan, most would need to be redeployed to the continental U.S. — but even then, the complex logistics and enormous expenses could result in units being decommissioned and disbanded altogether.

The cost of the U.S. military presence in Japan is around $5.5 billion a year, roughly half of which is devoted to U.S. paychecks, health care expenses and related costs. Through the 2015 five-year host nation support agreement, the Japanese government contributes around ¥197 billion annually in direct support (over $1.8 billion, depending on which expenses are included in the calculation, as well as currency exchange rates). That’s a more generous arrangement than with any other U.S. ally.

Policymakers in Washington and Tokyo should also consider that U.S. troops were introduced into Japan in the aftermath of a devastating world war. Should they be removed, given the depth of local opposition to their presence, this would likely be a one-shot deal; even if future leaders decided to reverse the decision, it is questionable whether U.S. forces could ever be reintroduced.

Nor should we forget the consistent public pronouncements of Japanese leaders that, insofar as Japan can rely on the U.S. nuclear umbrella and the Japan-U.S. alliance, Japan has no incentive to build and deploy nuclear weapons. By the same token, this implies that Japan’s leadership might need to undertake an agonizing reappraisal of the situation should Japan no longer be able to rely on the nuclear umbrella and alliance.

It is therefore imperative for Washington to reassure Tokyo that the alliance, and with it the nuclear umbrella, are rock solid. In fact, the U.S. government takes great pains to do just this. For example, in June the two governments conducted the latest round of the U.S.-Japan Extended Deterrence Dialogue in Minot, North Dakota, site of Minot Air Force Base, which hosts elements of the U.S. Air Force Global Strike Command.

The EDD has been held on a regular basis since 2010; the two governments use it as a forum to engage in broad and ongoing discussions on deterrence issues within the Japan-U.S. alliance. However, continuing back chatter among the Washington policy community on the utility and longevity of the security alliance may serve to dilute or even nullify the effect of such routine, if well-intentioned, bureaucratic channels.

The surest way to tamp down speculation and negativity about the alliance is to proactively separate out and deal with the granular concerns embedded in the inchoate rhetoric about the alliance.

Specifically, the question of whether Japan is paying its fair share for hosting U.S. forces — including for local base workers, utilities, training relocation and facilities improvement — should be addressed when Tokyo and Washington revisit the five-year host nation support agreement, last updated in April 2016. Rather than focusing on getting the best deal possible, Tokyo should be prepared to make every effort to be accommodating. This would be a prudent investment in the Japan-U.S. relationship.

More broadly, Japan should continue to move toward reciprocity in the alliance. Tokyo should address concerns voiced by some U.S. political leaders that the treaty is one-sided because the U.S. is pledged to defend Japan against attack, but Japan is not similarly obliged to assist the U.S. It can do so by enhancing its own deterrence capability and examining ways to expand Japan’s roles and missions.

Ultimately, however, Tokyo will have to make some hard choices about scenarios under which Japanese forces will defend U.S. forces if the latter are attacked. In this way, defending Japan will become more defensible.

Thomas Cynkin is a former U.S. charge d’affaires to the Conference on Disarmament in Geneva. He is vice president of the Daniel Morgan Graduate School of National Security.

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