In the wake of North Korea’s most recently reported nuclear test, which took many by surprise—because the yield was much larger than most analysts expected and because North Korea claimed it was a hydrogen bomb or a thermonuclear weapon that is the same type that the U.S. and Russia have—Secretary of Defense James Mattis assured Japanese Defense Minister Itsunori Onodera that “the United States’ commitment to defend Japan, including the U.S. extended deterrence commitment, remains ironclad.” To be sure, this is reassuring to Japan. But why does Japan need such a commitment? And, more importantly, why doesn’t Japan have an ironclad commitment to defend itself? Certainly, Japan would be better off if it didn’t have to depend on the U.S. And America would be better off with a strong, capable ally.

In the aftermath of World War II, there were good reasons for the U.S. to assume the mantle of defending Japan. First and foremost, the U.S. wanted to prevent Japan from becoming an aggressive military power—and the Japanese agreed—as a means to avoid a replay of war in the Pacific. Second, the reality was the Japan had been ravaged by war and—much like America’s European allies—needed the U.S. to provide stability and act as a counterweight to the Soviet Union and, to a lesser degree, China, as it rebuilt its economy.

But that was then and this is now.

Today, Japan is the third largest economy in the world (only the U.S. and China are bigger) with a gross domestic product (GDP) of $4.9 trillion. The Central Intelligence Agency estimates North Korea’s economy to be about $40 billion, which would place it in between Tunisia and Jordan—ranked 86th and 87th, respectively—on the World Bank’s list (the World Bank does not include North Korea on its list because it cannot confirm the country’s GDP). But with an economy more than 100 times larger than North Korea’s, Japan can easily afford to pay for its own defense—and it’s long past time for our wealthy ally to shoulder the responsibility of its own national security.

As a move in that direction, the Japanese Ministry of Defense recently requested its largest budget ever for fiscal year 2018—$48 billion, which is more than North Korea’s total economy. North Korea’s defense spending is believed to be about $10 billion, which is somewhere between 20 and 25 percent of its GDP. Just as Japan’s economy eclipses North Korea, so does its defense spending—by more than 4-to-1.

Put simply, if a rich country like Japan cannot defend itself against a very poor country like North Korea, there is something very wrong. Especially when Japan’s Self Defense Forces (SDF) are considered one of the best militaries in the world. According to John T. Kuehn, a professor of military history at the U.S. Army Command and General Staff College, “Pilot for pilot, ship for ship, Japan can stand toe to toe with anybody.”

What Japan is most worried about, of course, is the threat posed by North Korea’s nuclear weapons and ballistic missiles. Their recent defense budget request reflects that concern, with tens of billions of yen (more than $600 million) for Standard Missile-3 missiles to intercept ballistic missiles in space and Patriot PAC-3 missiles to intercept warheads in their terminal phase inside the atmosphere. At least the Japanese have a willingness to pay for such capabilities, rather than expecting that they should be given to them courtesy of U.S. taxpayers.

But even with missile defense, Japan continues to rely on extended deterrence via the U.S. nuclear umbrella to deter North Korea’s nuclear weapons. But whether extended deterrence will work is unclear. Is Kim Jong-un credibly convinced that the United States is prepared to risk Los Angeles for Tokyo? Does the Japanese government believe the U.S. would do so? And, most important, is that a price Americans should pay for a rich ally such as Japan?

Just as Japan is considering amending its constitution to explicitly allow for armed forces and avoid any contradiction between the constitution and Japan’s SDF (Article 9 states that “land, sea and air forces, as well as other war potential, will never be maintained”), perhaps it is also time to consider whether the best way for Japan to deter North Korea’s nuclear capability is with its own such capability—because the reality is that the only way to deter nukes is with nukes.

While we rightly remain concerned about nuclear proliferation, what is worse: A country like North Korea with a nuclear monopoly able to threaten its neighbors and hold them hostage? Or allowing Japan—a democratic U.S. ally—to have its own nuclear deterrent to offset Pyongyang rather than risking Los Angeles or Seattle to save Tokyo?

Nonproliferation advocates would be aghast about the prospect of more countries with nuclear weapons, but Japan as an effective nuclear counterbalance to North Korea has some precedent. Both India and Pakistan have nuclear weapons and have managed not to vaporize each other. There is some evidence that nuclear weapons have actually had a stabilizing effect on Indian-Pakistani relations, which runs counter to nonproliferation expectations. For example, does the fact that both India and Pakistan have nuclear weapons prevent violence related to the Kashmir dispute from erupting into war between the two countries?

And the reality is that although Japan is a signatory to the Nuclear Nonproliferation Treaty, which prohibits it from having nuclear weapons, it has a “bomb in the basement,” with de facto capability to build nuclear weapons since the 1980s when it decided to embark on a nuclear energy program with a plutonium breeder reactor and a uranium enrichment plant. Building an actual nuclear deterrent would not be a huge leap.

The issue isn’t whether Japan should have nuclear weapons or not. The issue is whether Japan should take primary responsibility for itself. If it doesn’t, then the U.S. will forever need to provide an ironclad commitment to defend an ally who is more than capable of defending itself.

Charles V. Peña is a senior fellow with Defense Priorities. He has more than twenty-five years of experience as a policy and program analyst and senior manager, supporting both the Departments of Defense and Homeland Security. Peña is the former director of defense-policy studies at the Cato Institute and author of Winning the Un-War: A New Strategy for the War on Terrorism.