China’s reported test of a nuclear-capable hypersonic weapon has raised alarm about the vulnerability of the U.S. to missile attacks by nuclear-armed adversaries. The U.S. should be vigilant about emerging threats, but pouring more money into unproven missile-defense technologies isn’t the answer. America’s aim should be to keep its missile-defense capabilities aligned with both fiscal reality and the country’s strategic interests.

Since the early 2000s, America’s missile-defense program has been geared to defend both the U.S. homeland and some overseas military assets from limited missile strikes. That has meant building defenses strong enough to stop an attack of the kind North Korea might contemplate, but not so large that they’d be both unaffordable and destabilizing. By making Russia and China less certain of the effectiveness of their respective arsenals, an expansive missile defense system could cause the U.S.’s competitors to pursue more nuclear weapons – potentially setting off an arms race that would drain U.S. resources and make the world more dangerous.

The U.S. currently has 44 ground-based missile interceptors in Alaska and California, designed to stop a limited intercontinental ballistic missile attack. Under the Trump administration, the U.S. canceled plans to update this system and launched a new one, known as the Next Generation Interceptor program, with the intention of fielding 64 interceptors in all by 2028. The U.S. also has three dozen ship-based ballistic missile-defense systems deployed on naval vessels protecting U.S. interests in Asia and Europe. Another anti-missile program, Terminal High Altitude Area Defense, focuses on short- and intermediate-range rockets. THAAD batteries are positioned in South Korea, Guam and Hawaii, among other places.

The government has spent at least $200 billion on missile defense over the last three decades. It’s unclear whether this has made the country any safer. Of 19 tests of ground-based mid-course interceptors conducted since 2001, only 11 have worked. The system has been used twice in simulated attacks by an ICBM, most recently in 2019. The Pentagon declared both tests successful, but neither was conducted under warlike conditions and the dummy ICBMs were less advanced than North Korea’s weapons. A Government Accountability Office report last year found that over the previous decade, the Pentagon’s Missile Defense Agency has postponed or scrapped 63 percent of its planned tests, which doesn’t inspire confidence.

U.S. officials have nonetheless pressed on. In 2019, then-President Donald Trump vowed to destroy “any missile launched against the United States – anywhere, anytime, any place,” and launched new efforts, including putting interceptors in space. Such technologies are unlikely to be operational anytime soon. Meanwhile, China and Russia have planned larger arsenals to evade any new U.S. defenses.

The hypersonic glide vehicle tested by China is a new complication. It would, in theory, be able to maneuver around U.S. detection systems and travel to the U.S. over the South Pole, far beyond the reach of Alaska’s ground-based interceptors. The Pentagon has requested $250 million to speed up development of weapons that can shoot down hypersonic missiles. This could cause China to respond by building more of them. And there’s no guarantee that defenses against hypersonic missiles would perform any better than ground-based interceptors have against ICBMs. Congress would be wise to restrain spending on hypersonic missile defense until research affirms its viability.

When it comes to defending against limited strikes on allies and military assets overseas, the cost-benefit calculation is more favorable. The U.S. should invest in upgrading the sea-based Aegis weapon system, which has historically performed well. It should complete long-delayed plans to build an onshore Aegis installation in Poland, alongside a similar site in Romania, to bolster Europe’s defenses against possible Iranian or Russian aggression. And it should expand technical support to Japan and South Korea to help them develop their own sea-based defenses.

Missile defense has the potential to help the U.S. counter the threat posed by rival militaries, but it’s not a substitute for traditional deterrence and arms control – and it should not be allowed to jeopardize them. Maintaining a credible but limited missile-defense capability, rather than spending crippling sums on ambitious new systems, is the best way to protect U.S. interests and allies.