Russia has tested a new missile-defense system. And while details of the new interceptor are difficult to confirm, it’s possible Moscow has take a huge step toward deploying a missile shield similar to America's own, much-more-sophisticated shield.

Even under the most generous assumptions, however, the Russian missile-defense probably shares a fundamental weakness with its American counterpart—an inability to stop the most powerful, long-range rockets.

Regardless, Moscow’s new missile shield could further destabilize U.S.-Russian relations by prompting the Pentagon to double down on countermeasures. In other words, an arms race.

The missile-shield test took place at the Sary-Shagan training ground in Kazakhstan. “The new modernized anti-missile defense system successfully accomplished the task and struck the conventional goal at the set time,” Col. Andrey Prikhodko, deputy commander of Russian air defense forces, said in a Nov. 24 statement.

According to multiple experts, the interceptor in the test appears to be part of a modernized version of the A-35 system, which the Kremlin installed in a ring around Moscow in the 1970s. The Anti-Ballistic Missile Treaty, which the United States and Russia signed in 1972, allowed each country to possess no more than 200 defensive missile-interceptors.

As installed, the A-35 included 16 large, nuclear-tipped SH-11 interceptor missiles and 68 smaller SH-08 missiles, also with atomic warheads. Cued by powerful radars, the rockets would explode high over Moscow during the initial stages of a nuclear war, potentially destroying incoming American intercontinental ballistic missiles.

Moscow deactivated the SH-11s after the fall of the Soviet Union, but the SH-08s remained in use. Observers have long expected the Kremlin to upgrade the missiles.

Leaving aside the dubious wisdom of triggering a nuclear blast to prevent a nuclear blast, it was never clear that the A-35 would actually work. Soon after Russia installed the system, the Pentagon devised a scheme to overwhelm the Russian missile shield with a devastating barrage of more than 100 ICBMs. “The U.S. reacted very robustly,” Hans Kristensen, a nuclear expert with the Federation of American Scientists, told The Daily Beast.

The United States unilaterally quit the Anti-Ballistic Missile Treaty in 2001, freeing up the Pentagon to develop more sophisticated and numerous missile defense. Russia called the move a mistake, and experts warned that a new missile-defense race could destabilize relations between the two powers by undermining mutual nuclear-deterrence.

That's exactly what has happened. As the United States and its closest allies install sea- and land-based missile shields in Alaska, California, South Korea, Japan and Eastern Europe, Russia has responded with an avalanche of new and more powerful nukes, some of which violate long-standing treaties.

“Russia is developing new nuclear weapons delivery systems, some of them potentially destabilizing—and countering U.S. missile defenses is a primary reason for that,” Laura Grego, a nuclear expert with the Union of Concerned Scientists, told The Daily Beast.

Now Russian anti-missile efforts could spur the United States to develop ever-more-powerful nukes of its own. “Future Russian anti-ballistic missile capabilities are already being used by the U.S. military to justify upgrading the U.S. ICBM force,” Kristensen pointed out.

While the strategic and diplomatic implications of Russia’s missile shield are clear, the system’s actual capabilities remain a mystery. For one, it’s possible the new interceptor swaps out the old atomic warhead for a non-nuclear one—or none at all.

The wording of the Kremlin’s announcement could imply that the interceptor physically struck its target instead of exploding near it. The latest U.S. missile-defenses use these so-called “hit-to-kill” interceptors that rely on the physical force of direct contact for their destructive force, as opposed to exploding.

If Russia has developed such an interceptor, it “would mark a significant advance in Russian strategic missile-defense technology,” Greg Thielmann, a missile expert and former Senate staffer who now sits on the board of the Arms Control Association, told The Daily Beast.

But even a U.S.-style, hit-to-kill missile-interceptor would be useless against the biggest ICBMs, to say nothing of a barrage of big ICBMs. Large intercontinental missiles move too fast for any defensive system to reliably stop them, which is why the Pentagon admits its own missile shield possesses “limited capability to defend the U.S. homeland from small numbers of simple intermediate-range or intercontinental ballistic missile threats.”

After decades of development, missile shields are still mostly symbolic. They can’t stop a determined nuclear attack. But in spurring a destabilizing arms race, they can make a large-scale nuclear war more likely. With its new missile-interceptors, Russia could be racing faster than ever before.