There is no more urgent threat to the global nuclear nonproliferation order than North Korea’s accelerating and unconstrained nuclear and ballistic missile programs. Pyongyang is estimated to possess enough nuclear explosive material for at least 10 nuclear warheads, and in all likelihood already has the capability to deliver some of these weapons on its arsenal of short- and medium-range ballistic missiles. By 2020, some experts believe Pyongyang may have enough fissile material for 100 warheads.

With more nuclear tests, North Korea can further refine its warhead designs to increase the explosive yield and further develop a lighter, more compact warhead to fit atop ballistic missiles. North Korea conducted two nuclear tests last year and its next nuclear test explosion, which would be its sixth, could happen at any time.

Since Kim Jong-Un took power in December 2011, North Korea has conducted 78 ballistic missile tests and continued development of a new generation of solid-fueled missiles (which can be fired more quickly than their liquid-fueled counterparts). In the past few weeks alone, North Korea has successfully tested a new type of mobile, solid-fueled medium-range ballistic missiles (MRBM) and a new type of intermediate-range ballistic missile (IRBM) capable of reaching the U.S. military bases on Guam. While North Korea has yet to demonstrate a capability to strike the United States with a nuclear-armed intercontinental ballistic missile (ICBM), it could begin flight-testing such a missile as soon as this year.

These developments have not surprisingly drawn attention to U.S. missile defense capabilities and prompted calls for the Trump administration to build more and new types of defenses. Yet while missile defense has a role to play as part of a comprehensive strategy to combat the North Korean missile threat, it’s neither as capable nor as significant as many seem to hope. As the Trump administration undertakes a major review of missile defense policy this year, it would do well to recognize that rushing to augment the U.S. missile defense footprint is misguided and could actually increase instability and the risk of war on the Korean peninsula.

A Mammoth Investment, But For What?

According to Missile Defense Agency estimates, Congress has appropriated roughly $190 billion for the agency’s programs between fiscal years 1985 and 2017. That total does not include spending by the military services on programs such as the Patriot system or the many additional tens of billions of dollars spent since work on anti-missile systems first began in the 1950s.

For nearly two decades, U.S. ballistic missile defense policy has sought to protect the homeland against limited long-range missile strikes from states such as Iran and North Korea, but not major nuclear powers Russia and China, since that mission would be technically infeasible, prohibitively costly, and strategically destabilizing. The United States has also pursued programs to defend U.S. troops and facilities abroad, and some close allies, from attacks by ballistic missiles.

The overall U.S. missile defense effort enjoys strong bipartisan support in Congress. Additionally, many U.S. allies place a high value on missile defense cooperation with the United States.

And yet, according to the Defense Department’s independent testing office, existing U.S. missile defenses possess only a “limited capability” to defend the U.S. homeland, troops deployed abroad, and U.S. allies from small numbers of ICBMs, IRBMs, and MRBMs. Their capability against short-range ballistic missiles ranks a bit better at “fair.” Apart from the point-defense Patriot system, no systems in the current U.S. arsenal of ballistic missile defenses have been used in combat. For these limited fruits, America’s costly pursuit of missile defenses has also been a decades-long irritant in the relationship with Russia, and increasingly in recent years, China.

Obama’s Missile Defense Bet

Upon taking office in 2009, the Obama administration took steps to curtail the Bush administration’s rush to expand the U.S. homeland missile defense footprint and instead place greater emphasis on regional defense, particularly in Europe. However, while continuing to invest in regional defense, the Obama administration took its foot off the homeland defense brake in its second term, in large part in response to North Korea.

The Defense Department announced in March 2013 that it would augment the ground-based midcourse defense system in Alaska and California, which is designed to protect the United States against limited, long-range missile strikes, by increasing the number of interceptors from 30 to 44 by the end of 2017. The administration took this step despite serious concerns about the technical viability of this system, which was rushed into service in 2004 by the Bush administration. The system has a flight intercept test record of less than 50 percent and has yet to be tested against an ICBM-class target. The first test against such a threat is scheduled for tomorrow (May 30).

The administration also oversaw the deployment of additional regional missile interceptor and sensor capabilities to allies in Northeast Asia in response to North Korea, including the deployment of the terminal high altitude area defense (THAAD) system to Guam and South Korea and two advanced radars to Japan.

These efforts were insufficient for Republicans lawmakers and national security experts. They criticized the Obama administration for reducing funding for missile defense, canceling promising programs, and failing to more aggressively expand strategic and regional defenses. These same voices pushed legislative proposals to build a third ground-based midcourse defense site in the eastern United States and begin research and development on interceptors in space. In addition, the Republican-controlled Congress last year voted to expand the declared role of U.S. homeland defenses beyond “limited” defense against North Korea and Iran, opening the door to countering the strategic deterrence forces of Russia and China.

Trump Takes Over

Earlier this month, pursuant to direction from President Donald Trump and Congress, Defense Secretary James Mattis formally announced the beginning of the department’s Ballistic Missile Defense Review, which will take a wide-ranging look at missile defense policy and strategy. The review is scheduled to be completed by the end of the year.

The president has provided few details about his vision for missile defense systems. A brief reference on the defense issues page of the White House website states, “We will … develop a state-of-the-art missile defense system to protect against missile-based attacks from states like Iran and North Korea.”

The Trump administration appears to recognize the obvious unpalatability of most military options to deal with the North Korean threat, such as attempting to destroy North Korea’s nuclear weapons and facilities or returning U.S. tactical nuclear weapons to the Korean peninsula. Beefing up missile defenses is thus likely to be viewed favorably by the administration as a way to look tough and attract bipartisan support.

The administration’s review could consider a number of options to expand U.S. defenses. These include the deployment of additional ground-based midcourse defense interceptors and sites, the acceleration of advanced missile defense technology efforts such as lasers to destroy missiles in their early stages of flight, and research and development on space-based interceptors. The administration might also increase regional defenses in Europe and Asia, though it is noteworthy Trump has demanded NATO countries to pay more for their defense, and specifically called on South Korea to pay for the THAAD battery deployed there. Key Trump advisors and nominees have publicly expressed support for some or all of these goals. And since the election, numerous Republican lawmakers and some Democrats, sensing an opportunity, have urged the new administration to put its foot on the accelerator of missile defense.

In addition to expansion, the Trump administration could also choose to more aggressively showcase U.S. missile defense capabilities, such as by shooting down North Korean ballistic missiles during their flight tests. The Pentagon is reportedly considering this option and has briefed it to Congress.

Capabilities Overstated

Prudent investments in missile defense continue to make sense as part of the U.S. response to North Korea and other challenges. There may also be a case for targeted increases in certain efforts, especially in the areas of improving sensor capabilities to discriminate real warheads from decoys and countermeasures — a major unsolved obstacle confronting U.S. defenses — and limited cruise missile defense. But more realism is needed about the limitations of defenses and the longstanding obstacles that have prevented them from working as intended. Missile defense does not provide an escape route from the vulnerability of our allies, deployed forces, and citizens in the region to North Korea’s nuclear and conventional missiles.

For example, though Gen. Lori Robinson, the head of U.S. Northern Command, told the Senate Armed Services Committee last month she is “extremely confident” in the ability of the ground-based midcourse defense system to “intercept an ICBM should it reach our homeland,” the Pentagon’s independent testing office assesses that ground-based midcourse defense system only has a partial and as yet undemonstrated capability to defend the homeland against small numbers of simple ICBMs and that the reliability of the system is low. The performance of the ground-based midcourse defense system in testing has actually been getting worse over time when it should be getting better. Only one of the past four intercept tests have been successful. These failures look even worse given that tests of the system occur in a controlled, scripted environment, meaning the defense is provided with information ahead of time that no real adversary would ever provide.

Moreover, the single THAAD battery that recently became operational in South Korea is positioned too far south on the Korean peninsula to be able to protect Seoul. And it’s difficult to judge the ability of the battery to protect other parts of the country without knowing how many interceptors are deployed, how quickly interceptors can be reloaded, and how many incoming missiles the system can handle at one time. The Missile Defense Agency told me these details are classified. Meanwhile, the THAAD battery deployed on the island of Guam designed to protect the U.S. military base there against intermediate-range ballistic missiles has yet to be tested against such a missile.

While U.S. homeland and regional defenses might have a chance of shooting down missiles that travel within the defended area of those systems, shooting down a North Korean missile on a test trajectory is an entirely different and even more difficult challenge.

In the case of a potential North Korean ICBM test, only the ground-based midcourse defense system is designed to intercept such a missile. But unless the test launch travels on a trajectory similar to what North Korea would actually use to shoot at the United States — a gamble Pyongyang is unlikely to take — the system will not be able to engage it, as it is postured to defend the United States and not the open ocean. Shooting down a North Korea medium- or intermediate-range missile test might be possible using SM-3 interceptors launched from Aegis ships in the region, but would be a highly demanding task and entail a significant amount of guesswork, as the ships would have to be in the right place at the right time to stop a test at sea. Doing so also would mean taking them away from optimal positions to defend actual targets on land.

Attempting to shoot down a non-threatening missile test would be hugely provocative act and supply invaluable data to adversaries. A miss, which is more likely than an intercept, would be embarrassing and undermine confidence in U.S. defenses. For these reasons attempting to shoot down such a test would appear to be a highly risky decision at best. Furthermore, despite much speculation in the press about the U.S. ability to hack North Korean missile tests, the data shows that North Korea’s missile tests are succeeding at a high rate and that the failures are concentrated in new systems that had not been previously tested.

Also, we sometimes forget North Korea gets a vote. As of 2015, the Pentagon estimated that North Korea possessed over 100 launchers for ballistic missiles and that number has likely grown since then. North Korea has made significant progress in its ability to design and build launchers and missiles indigenously, which will allow it to more easily expand its missile force.

North Korea is also taking steps to overwhelm and evade U.S. defenses through such steps as developing solid-fueled mobile missiles, practicing to launch multiple missiles at the same time (known as salvo launches), developing submarine-launched ballistic missiles, and experimenting with maneuverable reentry vehicles. It could also pursue the development of decoys and countermeasures specifically designed to fool U.S. missile defenses. While imperfect defenses might be able to limit damage against conventionally armed missiles, the devastation that would result from even one nuclear weapon landing on Seoul or Guam gives North Korea a significant deterrent capability. And it wouldn’t even need to come to this: North Korea possesses hundreds of artillery pieces that hold Seoul at risk and against which the United States and South Korea have no defense.

Indeed, Pyongyang is much more likely to be deterred from using its nuclear-tipped missiles by the sure knowledge that the U.S. military response would bring the Kim regime to a bloody end than by the prospect that some of its missiles might be intercepted.

U.S. military officials have been increasingly vocal in recent years about the difficulty of keeping pace with adversary missile developments, noting repeatedly that the current U.S. missile defense strategy of countering adversary missiles with expensive interceptors is “unsustainable,” and have pushed for the development of new technologies to attempt to reduce costs and increase effectiveness.

More is Not Always Better

It is against this backdrop that the Trump administration will decide whether to embark on a major expansion and acceleration of the U.S. missile defense effort. While North Korea is advancing its capabilities, a missile defense buildup would carry more costs than benefits.

Deploying more flawed ground-based midcourse defense interceptors in Alaska or building a third site in the eastern United States is not a winning strategy to stay ahead of the North Korean threat. Quantity is not a substitute for quality.

Given the low reliability of the ground-based midcourse defense system’s interceptors, the Pentagon’s current “shot doctrine” for the system calls for launching as many as five interceptors at a single ICBM, meaning the planned force of 44 interceptors could handle at most nine ICBMs.

Purchasing five interceptors (at an estimated cost of at least $70 million per interceptor) for every additional North Korea ICBM is the opposite of cost-effective. And if one interceptor isn’t capable of doing its job for reasons inherent to the design of the system, chances are that the next one can’t, and the next one, and so on. While the ground-based midcourse defense system is finally being tested against an ICBM target, its salvo capability where two interceptors are in flight at the same time has also not been tested.

Any consideration of building and deploying additional homeland interceptors or interceptor sites should wait until a new ground-based midcourse defense kill vehicle under development is successfully tested under operationally realistic conditions (including against ICBM targets and realistic countermeasures). The first test of the new kill vehicle under these conditions is not scheduled until 2020 and deployment isn’t scheduled until 2022. If the United States is going to invest scores of billions in missile defense, then it should work as intended.

In addition, future deployments of new capabilities should not be schedule-driven, but based on the maturity of the technology and successful testing under operationally realistic conditions. Accelerating development programs risks saddling them with cost overruns, schedule delays, and test failures, as has been the case with previous missile-defense programs.

A more disciplined approach should apply to buttressing theater capabilities in East Asia. While deploying additional THAAD batteries and land- and ship-based SM-3 interceptors to the region may help to reassure allies, they will not meaningfully reduce their vulnerability to nuclear attack and will only strengthen North Korea’s resolve to increase the quantity and quality of its missiles forces.

The impact of an expansion of U.S. missile defense capabilities on Russia and China must also be considered. While the intention behind U.S. missile defense is not to threaten Russia’s or China’s ability to strike the United States with nuclear weapons, both Russia and China fear otherwise. As the bipartisan Congressional Commission on the Strategic Posture of the United States noted in its 2009 report, “China may already be increasing the size of its ICBM force in response to its assessment of the U.S. missile defense program.” An expansion of U.S. capabilities, especially if combined with an expansion in the declared role of missile defenses beyond defense against limited attacks, would almost certainly exacerbate Russian and Chinese concerns, prompting them to take steps that would undermine U.S. security and that of our allies.

At the same time, both Russia and China are modernizing and expanding their air and missile defense systems, as well as their ability to counter defenses. Neither the United States, Russia, or China appear to take the concerns of their competitors about missile defenses sufficiently seriously to prevent increased risks of arms racing and instability. The United States should continue to try to reassure its near-peers of the limited purpose of its missile defenses and engage in more robust discussions with these countries on how missile defense developments are increasingly connected and moving in possibly destabilizing directions — and discuss steps that can be taken to mitigate these negatives.

There is still another problem with pushing the accelerator on missile defense, a risk exacerbated by the Trump administration’s more muscular approach to North Korea, which includes blustery threats and talk of a military buildup in the region.

Misplaced overconfidence in missile defense could prompt Trump think he can escalate in response to another North Korea nuclear or missile test or other provocation without having to worry about a potential North Korean nuclear response. This would greatly increase the risk of conflict on the Korean Peninsula.

The United States must use the full range of diplomatic, economic, and security tools at its disposal to reduce the threat posed by North Korea pursuant to the goal of phased denuclearization, beginning with a negotiated freeze on nuclear and missile testing. Missile defense can’t provide an escape from the reality that North Korea is improving its nuclear arsenal.

Kingston Reif is the Director for Disarmament and Threat Reduction Policy at the Arms Control Association. You can follow him on Twitter at @KingstonAReif.

Image: U.S. Army photo