Homeland missile defense faces an uncertain future. The United States deploys 44 ground-based interceptors to Alaska and California and a global sensor network to defend the homeland from a limited attack. But as these systems age and the foreign missile threat grows, the U.S. needs to commit to ensuring an adequate missile defense for the future.

A strong missile defense offers many benefits. Most importantly, it can save hundreds of thousands, if not millions, of American lives, from a limited nuclear attack.

It also serves as a deterrent. By lowering the probability that an attack will succeed, it forces states like North Korea to think twice before pushing the launch button.

Other benefits include giving our military greater freedom to defend our allies (by lowering the probability of a retaliatory homeland attack) and strengthening our hand in diplomatic negotiations (because our adversaries know we can to mitigate their threats).

Despite the multiple advantages of a strong homeland missile defense, plans to achieve that goal—first articulated in 1983—have not been realized. What started as President Ronald Reagan’s Strategic Defense Initiative, a comprehensive plan to render any missile attack obsolete was eventually scaled back to President Bill Clinton’s plan to deploy only 100 ground-based interceptors. It was not until 2004, when the urgently emerging North Korean threat became apparent, that interceptors were deployed as part of the Ground-based Midcourse Defense (GMD) system.

There has not been significant progress on expanding the GMD system since, even though the threat has increased.

North Korea continues to improve the size, sophistication and range of its missile arsenal. Eventually, it could arm its missiles with countermeasures like decoys and penetration aids to evade U.S. missile defenses. Meanwhile, the kill vehicles on today’s ground-based interceptor fleet, now over a decade old, continue to age and face obsolescence issues. Senior defense leaders expect these two issues—increasing threat and aging defenses—to converge around 2025.

The Pentagon’s Redesigned Kill Vehicle program would have bridged this gap until a next-generation interceptor was developed. It also would have added 20 interceptors to our defenses. But that program was abruptly cancelled last year.

At best, the Pentagon’s Next Generation Interceptor (NGI) program will not begin to replace aging interceptors and add capacity to the GMD system before 2028. Until then, the very real prospect of having insufficient capability to defend against a rogue nation should prompt serious concern within Congress and the administration.

The GMD system is also underprepared for a potential Iranian missile attack aimed at the East Coast. Interceptors in Alaska are technically capable of defending the entire United States. However, an East Coast missile defense site would significantly increase the probability of successful intercept.

The administration has identified the need to deploy sensors to space for the purpose of “birth-to-death” missile tracking. Yet this program, the Hypersonic and Ballistic Tracking Space Sensor, has been plagued by insufficient funding requests and program turbulence.

What’s needed to stabilize our homeland missile defense is more money and numerous steps. To get the ball rolling, Congress and the administration should focus on the following.

First, the space sensor layer program needs to be sufficiently funded to move up its deployment as much as possible. Being able to see the threat—including emerging threats like hypersonic missiles—must be a prerequisite to advanced shooter capabilities. Fortunately, both the House and Senate have authorized more funding for this program than the Pentagon requested.

Second, the United States must invest heavily in keeping the current ground-based interceptor fleet viable until the NGI can be brought to the field. Last year, Congress provided additional funding to extend the service life of the current 44 interceptors. This effort should continue in future years as part of a comprehensive effort to maintain the GBI fleet.

The Defense Department must prioritize addressing this near-term problem before other important, yet less urgent issues like East Coast defense or boost-phase intercept technology.

Third, the United States should proceed with the administration’s plan to develop a homeland defense “underlay” using regional interceptor systems, but not as a replacement for short-term improvements to the existing interceptor fleet. Pursuing an underlay as a “back-up” option to shoot down incoming missiles is a worthwhile pursuit, but it could become too costly and time-consuming to “solve” the aging fleet problem.

The Defense Department has yet to put “math” to the concept of an underlay. Both the Senate and House defense policy bills would rightly require the Pentagon to begin answering critical questions about its plan before proceeding to the next steps.

The National Defense Strategy and the Missile Defense Review both identify homeland defense as the highest priority. It is therefore essential that homeland missile defense receive greater emphasis and a clearly defined future. The steps outlined above will put the Defense Department back on track.