By Troy Stangarone

As Donald Trump beings to lay out more of his thinking on U.S. foreign policy, one issue that is gaining attention is his suggestion that the United States should remove its nuclear umbrella from South Korea and Japan and that these nations should be allowed to develop their own nuclear deterrent. Implementing this policy would be problematic for a number of reasons related to U.S. security, the broader implications of the policy, and the ability to actually implement it.

Not surprisingly, journalist Anderson Cooper discussed this issue in detail with Donald Trump in the recent CNN Town Hall in the lead up to the Wisconsin presidential primary. While the full transcript of the discussion can be found here, the crux of the discussion focused on the contradiction between supporting nuclear non-proliferation and endorsing the idea of South Korea and Japan (and other nations) should develop nuclear weapons. For Trump three issues seemed to dominate his thinking on this issue. First, since other countries already have nuclear weapons, it is inevitable that South Korea and Japan will develop them eventually as well. Second, that in light of the current budget situation in the United States, Washington can no longer afford to pay to defend other countries. Lastly, he argued that the benefit to the United States of providing security to other nations is not worthwhile.

Is it inevitable that South Korea and Japan will develop nuclear weapons? As Mark Fitzpatrick of the Institute for International Security Studies points out, the United States’ nuclear umbrella and policy of extended deterrence have provided reassurances to Seoul and Tokyo about their security posture. Both countries would likely pursue a nuclear option if they believed that the security assurances of the United States were in doubt.

At the same time, both South Korea and Japan have refrained from developing nuclear weapons despite North Korea’s continued pursuit of weapons of mass destruction. If the possession of nuclear weapons by a neighboring state were an indicator of a country’s likelihood of developing nuclear weapons, one would have expected South Korea and Japan to already have done so. Ultimately, a Trump administration policy of weakening U.S. security commitments to Seoul and Tokyo would likely do more to encourage them to develop a nuclear weapons program than anything North Korea has done to date.

If the U.S. nuclear umbrella and extended deterrence can reassure U.S. allies and therefore also help to constrain nuclear proliferation, is Trump right to suggest that it is a burden that the United States can no longer afford? As Robert Samuelson at the Washington Post points out, the United States is wealthy enough to pay for domestic needs and a robust presence abroad. Since 1950, U.S. GDP has risen from $2.2 trillion to $16.3 trillion last year in inflation adjusted terms. At the same time, Japan’s per capita GDP is only 69 percent of the United States’ and South Korea’s less so. While a debate over the best usage of resources in any society is legitimate, the United States is clearly wealthy enough to meet its commitments abroad should society at large deem them to be beneficial.

More to Trump’s point about burden sharing, South Korea already contributes a great deal to the alliance in contrast to what he has suggested. Seoul provides 55 percent of the non-personnel costs for stationing U.S. troops in South Korea, including annual increases. It spends more on defense, 2.6 percent of GDP, than any other ally in Europe and Asia, and fields an active military of 630,000 troops through conscription. South Korea has also historically contributed troops to assist the U.S. in past wars and peace keeping missions than any ally other than the United Kingdom and a few others.

This brings us to the last of Trump’s arguments, that the United States does not benefit enough from its commitments abroad. Is this the case? As previously noted, U.S. commitments to our allies have helped constrain nuclear proliferation, but the United States benefits in other ways as well. U.S. commitments abroad provide necessary stability around the world to maintain the peace and order that helps to enable the international commerce necessary for U.S. prosperity. U.S. bases abroad also provide forward positioning to allow the United States to deal with military threats abroad before they endanger the homeland.

At the same time, the idea of allowing South Korea and Japan to develop nuclear weapons to lessen the burden on the United States would face a series of constraints and concerns. As we have noted on previous occasions, there are real economic and foreign policy constraints on South Korea developing a nuclear weapon. Many of these would apply to Japan as well.

Seoul and Tokyo would need to either violate their commitments to or withdraw from the Nuclear Non-Proliferation Treaty (NPT). If they, along with Saudi Arabia and other countries, did so as a result of Trump’s policy, it would likely be the end of the NPT and increase nuclear proliferation worldwide. This has significant security implications for the United States, especially as it relates to terrorism. As more states develop nuclear programs there will increasingly be more states with access to fissile material that a bad actor could utilize to threaten peace and stability.

More practically, even with U.S. support, other countries might decide to hold the line on nuclear non-proliferation. If that was the case, the Nuclear Suppliers Group would likely end shipment of nuclear fuel to South Korea and Japan, placing the United States in the awkward position of having to supply nuclear fuel to prevent power shortages in South Korea, though to a much lesser extent in Japan.

There could be economic consequences more broadly as well. As with prior efforts by states such as North Korea and Iran to develop nuclear weapons, Japan and South Korea could also face economic sanctions in the absence of a broader global agreement on nuclear proliferation.

Eliminating U.S. extended deterrence commitments to South Korea and Japan, along with Trump’s previous suggestions that he would withdraw U.S. troops if both countries did not pay more for their stationing, raises questions about how the United States would fulfill its obligations on the mutual defense treaties it has with both nations.

Lastly, one disconcerting question Trump’s policy would raise for policy makers in South Korea and Japan is whether he would abandon efforts to denuclearize North Korea and agree with Kim Jong-un that North Korea should be recognized as a nuclear weapons state?

Rather than reducing the burden on the United States and improving U.S. security, encouraging South Korea and Japan to develop their own nuclear deterrent would likely result in increasing instability in East Asia, declining U.S. influence with U.S. allies and in the region, and, more broadly, a lessening of U.S. national security interests.

Troy Stangarone is the Senior Director for Congressional Affairs and Trade at the Korea Economic Institute of America. The views expressed here are his own.

Photo from Gage Skidmore’s photostream on flickr Creative Commmons.