There are reports that, with his invasion stalemated and his army in tatters, Vladimir Putin might use chemical, biological, radiological or tactical nuclear weapons (WMDs) in Ukraine. The indications are that as part of a false-flag operation—perhaps involving an ammonia plant or prewar efforts to clean up Soviet-era bioweapons research facilities—the Russian military might accuse Ukraine of a WMD attack and then “respond” in kind. We should hope and pray Putin is just posturing or blustering. But since America and its NATO allies cannot base policy decisions on hope, the allies must prepare military options to forcefully and swiftly respond to such a contingency.

To its credit, the Biden administration appears to be doing exactly that. According to a New York Times report, the White House has “assembled a team of national security officials to sketch out scenarios of how the United States and its allies should respond if Russian President Vladimir Putin…unleashes his stockpiles of chemical, biological or nuclear weapons.” The team has been meeting since February 28.

It's far more preferable to prevent or deter Putin from using a WMD than to be forced to deliver a response to a WMD attack. That helps explain the leaks to the New York Times, as well as the signals allied leaders have been sending in recent days.

President Joe Biden promises a “severe price” and “severe consequences” if Russia uses WMDs. Defense Secretary Lloyd Austin warns of “significant reaction” from NATO to a Russian chemical attack.

German Chancellor Olaf Scholz told Putin in a recent phone call that the use of chemical weapons or bioweapons would be “unacceptable and unforgivable.” Polish President Andrzej Duda says Putin’s use of WMDs would be “a game changer.”

NATO Secretary General Jens Stoltenberg warns, “Any use of chemical weapons would totally change the nature of the conflict…Any use of chemical weapons is absolutely unacceptable, and will have far reaching consequences.” Ominously, he reports the alliance is delivering “equipment to help Ukraine protect against chemical, biological, radiological and nuclear threats.”

While Putin claims that Russia has destroyed its chemical weapons, Russia used chemical agents against Chechen rebels and has used chemical nerve agents to target regime enemies on foreign soil. Putin also aided and abetted Assad’s chemical attacks in the Syrian civil war. As Biden concludes, “He’s already used chemical weapons in the past, and we should be careful of what’s about to come.”

Less than two weeks before he ordered U.S. forces to begin the liberation of Kuwait, President George H.W. Bush dispatched Secretary of State James Baker to meet with his Iraqi counterpart and deliver a letter to Saddam Hussein. Part of that letter provides a roadmap for conveying to Putin America’s seriousness about the use of WMDs.

“The United States will not tolerate the use of chemical or biological weapons,” the letter bluntly explained, adding, “The American people would demand the strongest possible response. You and your country will pay a terrible price if you order unconscionable acts of this sort.”

In a similar way, Biden should quietly dispatch an emissary who knows the neighborhood—Gen. James Mattis commanded NATO’s Allied Command for Transformation, Secretary Robert Gates was a Soviet expert at the CIA throughout the Cold War, Gen. Phillip Breedlove commanded NATO—to impress upon one of Putin’s generals or spymasters that Putin has everything to lose if he uses WMDs and that he has something to gain if he stops this war. The president’s emissary should then remind his Russian counterpart that in the span of a month the war in Ukraine has killed between 7,000 and 15,000 Russian troops; that another 30,000 have been maimed or captured; that Russian generals are being killed in bunches; that Ukraine has destroyed 564 Russian tanks/armored vehicles, 62 Russian aircraft and a number of Russian warships; that Russia’s GDP is expected to shrink more than 10 percent this year; and that all of this has transpired without U.S. or NATO assets so much as even setting foot on Ukrainian soil or flying a single sortie through Ukrainian airspace.

And then, as Baker did in 1991, the president’s emissary should share a personal message from the leader of the Free World: “America will not tolerate the use of chemical, biological, radiological or nuclear weapons against Ukraine by the Russian military, its proxies or its intelligence services. If these weapons are used, deployed Russian military forces will pay a terrible price—worse than anything the Russian military has endured in your president’s unconscionable, unjustified war against Ukraine.”

This message could be underscored—for the benefit of Russian spies and satellites—by quietly surging an additional carrier strike group to the Mediterranean, repositioning missile-laden surface ships into the theater, forward-deploying B-1Bs and additional B-52s to Britain, and increasing the tempo and frequency of bomber flights over Eastern Europe. (B-52s have already flown along the Ukraine-Romania border in the weeks since Russia’s invasion.)

To be sure, there are lines we must be careful not to cross here, and there are risks if the U.S. and NATO become directly involved in Russia’s war.

Regarding the risks of direct involvement, there are many. Justin Bronk of the Royal United Services Institute cogently and succinctly details them here. Importantly, his comments are focused on the war remaining within the conventional threshold. In the event of a WMD attack, those risks would be outweighed by the risk of what Russia and other hostile regimes would do if the Free World allowed Putin to use WMDs without consequence. As President John Kennedy concluded during another crisis triggered by another reckless strongman in Moscow: “The greatest danger of all would be to do nothing.”

As to the lines we need to avoid crossing, Putin’s Russia is not Saddam Hussein’s Iraq or Moammar Qaddafi’s Libya. Russia is a full-spectrum military power bordering America’s closest allies, with the capacity to strike those allies and the U.S. with nuclear, conventional, aerospace and cyberspace weapons. Simply put, Russia poses an existential threat. That necessarily limits the options NATO can employ in response to a Russian WMD attack in Ukraine. But Russia’s status as a nuclear power doesn’t eliminate NATO’s options, and it doesn’t mean Putin should be comfortable with those options. (A Russian attack of any kind against a NATO member would be an act of war against the entire alliance, triggering NATO’s Article V collective-defense mechanism.)

NATO has a range of options, in the event of a Russian WMD attack in Ukraine, including:

-Delivery of antitank, antiaircraft and antipersonnel weapons systems to Georgia to enable its military to retake territories seized by Putin in 2008.

-Deployment of NATO peacekeeping forces into Moldova and/or Georgia, at the invitation of the host nation(s).

-Targeted strikes against Russian military units involved in the WMD attack inside Ukraine using standoff weapons launched from vessels operating in international waters in the Aegean Sea and/or Adriatic Sea and/or from aircraft operating in international airspace. Conducting such an attack from international waters and international airspace would provide a layer of protection to European allies concerned about a Russian counterattack.

-Missile strikes and airstrikes using those same standoff weapons systems against all Russian command-and-control nodes inside Ukraine.

-Missile strikes and airstrikes against Russian military targets across the whole of Ukraine.

-Simultaneous strikes targeting Russian command-and-control nodes in occupied Ukraine, occupied Georgia, Syria and Libya.

These options are, by definition, escalatory. However, they also are restrained in that they wouldn’t target or threaten Russian territory or the Putin regime. Putin’s military would recognize such signaling—especially if these options were laid out by the president’s emissary with the aim of deterring Russia from using WMDs.

Obviously, this is not an exhaustive list. NATO’s militaries and intelligence agencies possess numerous left-of-launch, cyber, electronic-warfare, drone and counter-space capabilities that could be brought to bear. But this list provides a sense of how NATO could respond to a WMD attack.

These responses are graduated, though they are not mutually exclusive. In the event of a Russian WMD attack, the U.S. and its allies could execute a mix of these and other options. And in the event of the worst kind of WMD attack—one involving a tactical or battlefield nuclear device—the Biden administration has made it clear “all bets are off” with regard to U.S.-NATO restraint in Ukraine.

Speaking of NATO, because of what could follow the punitive strikes outlined above, the NATO allies would need to be on the same page. All 30 NATO members wouldn’t have to participate—and couldn’t for that matter—but they might have to assent to the response. That said, several NATO allies would join such an effort. For those allies concerned about the need for some sort of cover or blessing from international law, Articles 11, 14, 51 and 52 of the UN Charter seem to check that box.

Describing NATO as “an antidote to chaos,” President Ronald Reagan urged the Free World to “unite to impose civilized standards of behavior on those who flout every measure of human decency.”

Putin’s invasion of Ukraine is awful; his use of WMDs would be worse. The U.S. and its NATO allies must be prepared for the worst—just as they were throughout the Cold War.