By powering the thing with a nuclear engine, Putin said Russia would give its cruise missile functionally unlimited range; nuclear power plants put out far more energy for far longer than conventional engines, which is why the American military uses them in submarines and aircraft carriers. Putin showed a computer-generated video of the Russian cruise missile circling the world, slipping around radar systems and arriving in North America from the southern end of the Pacific Ocean.

Putin also announced the nuclear torpedo — an underwater missile with a nuclear warhead — which he said had been tested and could travel vast distances underwater before striking an enemy along the coast.

Finally, he advertised an update to existing ballistic missile technology: a missle that can deploy multiple warheads, all of which enter the atmosphere at hypersonic speeds — up to 20 times the speed of sound — and could perform evasive maneuvers in flight before striking their targets.

The upshot, Coyle said, is that none of these weapons could ever be defended against with modern technology.

The whole point of the ABM was to ward off this sort of technology

“[The ABM] was really meant to short-circuit the arms race dynamic,” said Laura Grego, a senior scientist at the Union of Concerned Scientists’ Global Security Program.

At the time of the treaty’s signing, officials with fresh memories of the ballistic missile technology race that peaked in the 1950s and ’60s during the Cold War worried that missile defense technologies might provoke a new wave of arms escalation, she said.

“Deterrence requires you to be able to hold your adversary at risk,” Grego told Live Science. “Defenses interrupt that. By building a defense, rather than discourage your adversary, your adversary is likely to just build more so that they can get up and over your defense. And then you build more defense. So it’s an arms race cycle.”

When two states have nuclear missiles and missile defense systems aimed at each other, both are incentivized to strike first. Wait and go second, and your reduced missile arsenal — whatever remains after your enemy’s first strike — is more likely to crash ineffectively against their defenses. Go first, and you have a hope of doing enough damage to wipe out your enemy and ride out the return strike.

Missile defenses haven’t worked out the way Bush-era officials hoped

Keeping fired missiles at bay is a tall order. In fact, Bush never planned to build a missile defense that could ward off the full might of the Russian ballistic missile arsenal. Instead, he pitched missile defenses as a necessary measure to defend the United States against the more limited arms of “rogue states” like Iran, as Time reported in 2007. But, as ABC News reported, the defenses turned out to be both expensive and ineffective in practice, leading President Barack Obama to scale down the program in 2009.

As recently as January, a U.S. ballistic missile interceptor test ended in failure. That was the second such failure in under a year, even though, as arms control expert Jeffrey Lewis has pointed out on his podcast, these sorts of tests tend to take place during ideal conditions, very different from the situation one might expect in an actual nuclear emergency.

Even so, arms control experts largely agree that these tests have provoked Russia’s efforts to improve its methods for delivering a warhead to an American city.

“Putin’s announcement is a predictable reaction to the ongoing missile defense efforts of the United States. Now, it appears that the Trump administration is going to ramp up these defenses, increasing Russia’s concerns,” Lisbeth Gronlund, co-director of the Union of Concerned Scientists’ Global Security Program, said in an emailed statement.

“Both nations have now stated they will deploy new types of nuclear weapons,” she added. “Putin’s announcement further ratchets up what is clearly a new arms race between the two countries.”

American defenses were likely not the only factor prompting Russia’s decision, Grego cautioned, pointing out that internal politics can be as big a driver of announcements like this one as foreign policy. As Anton Troianovski pointed out in a Washington Post article, “Putin’s speech, less than three weeks before the Russian presidential election, represented an escalated level of martial rhetoric even by his pugnacious standards.”

Russian nukes learn to turn

As much as American missile defense systems tend to fail, the reason they work at all, Grego said, is that ballistic missiles follow fairly predictable trajectories.

“Ballistic missiles, true to the name, go on a ballistic trajectory,” she said. “So they use these powerful engines to get themselves moving really fast, but after the engines burn out, they’re just coasting.”

At that point, tracking, predicting and intercepting a ballistic missile’s trajectory becomes a straightforward question of precision and physics. Really difficult, extreme precision and physics that even the best American weapons engineers can’t achieve reliably. But straightforward nonetheless.

Russia’s newly announced weapons circumvent that problem entirely because all of them, one way or another, arrive without going in a straight line. The underwater torpedo, low-flying cruise missile and hypersonic weapon — wherever they might be along the track of development — are all able to avoid missile defenses by simply arriving along unexpected, untrackable routes.

Plus, the cruise missile flies low over land and ocean waves, below the effective reach of radar. The torpedo swims underwater. Even if somehow they could be tracked and predicted, nothing in the U.S. arsenal could catch up with them and strike them.

“We do not have capabilities against these kinds of systems and, as far as I’m concerned, never will,” Coyle said.

New tech won’t fix this tech problem

Coyle, Grego and Gronlund all cautioned against responding to Russia’s claimed technological advance by building new American gadgets.

“We Americans always hope that there will be a high-tech solution that will keep us from having to deal with an international problem like Russia,” Coyle said. “I’m hopeful that these developments will help us realize that there is no high-tech solution, and we simply need to sit down at the negotiating table and reach new treaties and a new peace.”

It’s important to recognize, Coyle and Grego both said, that in many respects, this new technology doesn’t change the Russian-American nuclear balance at all.

“Russia could hold everybody at risk in the United States,” Grego said. “It has enormous destructive potential even without these missiles. This is a new way of doing it, but it doesn’t essentially change the fact that the United States is vulnerable to Russia, just as Russia is vulnerable to the United States.”

The risk, Grego said, is that now Americans will feel “motivated” to counter these new Russian technologies with new American technologies.

“There’s a temptation to try to spend your way out of it, or try to ‘technology’ your way out of it, rather than addressing the real root question of ‘Why do we have these enormous nuclear arsenals, and why are we trying to structure our security around them?'” Grego said.