Vladimir Putin's potential use of nuclear weapons can't be dismissed

The question haunting Washington and other capitals is whether Russian President Vladimir Putin might resort to using nuclear weapons in Ukraine.

What would be his reasoning? What might be the consequences? And what can be done now to prevent Putin even from considering that use?

If the war in Ukraine continued to be a disaster for Russia, a desperate Putin might conclude only the nuclear option could favorably end the "special military operation." The costs could be too great to bear and could no longer be concealed from the Russian public. Or, Putin could become impatient and seek a decisive end to the war.

No matter how remote the possibility of Russian nuclear weapons use may be, those scenarios cannot be dismissed. Nor should reliance on Putin exercising self-deterrence because of the horrific consequences be the sole foundation for preventing a nuclear catastrophe.

What then must the United States and NATO be doing to prevent this contingency from arising? Should there be any distinction in response between a nuclear weapon employed as a demonstration shot doing little to no damage or in anger to obliterate a major city such as Kyiv and a substantial part of Ukraine's military?

Why would Putin believe that nuclear weapons would fulfill his objectives and not lead to a broader conflict? Since Putin reads history, he would be knowledgeable of the only wartime use of nuclear weapons. That might influence his thinking.

In August 1945, after a short meeting of his war council, U.S. President Harry Truman authorized the nuclear bombing of Japan. The intent was to "shock and awe" the Japanese high command to surrender unconditionally. Thousands of B-29s dropping hundreds of thousands of bombs on helpless Japanese cities could not force that. And based on Japan's possible suicidal resistance, the invasion plan for Japan, Operation Olympic, projected a million U.S. and allied casualties and many times that for the Japanese.

After Hiroshima was eviscerated, the Japanese war cabinet voted to continue the war. Two days later, a second bomb destroyed Nagasaki. The war cabinet remained divided. It took the emperor to break the tie. Japan capitulated.

Putin might think that destroying Kyiv, rather than relying on a demonstration shot, would achieve a similar outcome of "shocking and awing" Ukrainian resistance into surrender. And Ukrainian President Volodymyr Zelensky might be killed, leaving Ukraine leaderless. But given the resistance shown by the Ukrainian people, whereas suicidal Japan surrendered, Ukraine might not resist. What then?

And would Putin use more than a single weapon?

Regardless of how that question might be answered, the United States and NATO have no option except to prevent Putin from even considering the use of nuclear weapons. Retaliating in kind; striking Russia; and other options would be very dangerous and could escalate into a thermonuclear war. Thermonuclear weapons possess a thousand times more explosive power than a nuclear weapon.

While risky, the most effective preventative would be an immediate and overwhelming conventional air and missile strike entirely confined to Ukraine. The objective would be to disrupt and cripple Russia's military in Ukraine. Key targets would be the logistics bases, including the Kerch bridge linking both shores of the Sea of Azov, increasing from hours to days the time it would take for resupply by road.

Russian military forces, including in Crimea and the Black Sea Fleet would also be fair game. The result would turn the tide of war in Ukraine's favor. These strikes would only take place if or after Russia used a nuclear weapon. And the Russian military understands that the United States and NATO have the military wherewithal to accomplish this mission. This option reinforces that understanding.

Given the battering that the Russian military has been taking, such a conventional counterstrike would further devastate it, effectively ending the offensive. Risky? Yes. However, what other options beyond self-restraint would assure nuclear weapons would not be used by Putin?

Some argue that the three levels in the Russian nuclear chain of command could prevent Putin's orders from being carried out. Perhaps. But believing that Putin's directives would not be followed would be a classic failure. Contingency planning must cover the case of Russian nuclear weapons.

This leaves the larger question unanswered of how this war ends, if it does. Focus has been on providing what Ukraine needs to halt this aggression in a timely fashion. Yet, more emphasis is needed on the exit strategies to stop the fighting and end the war on terms that are remotely just to Ukraine. And where is that being done?

Harlan Ullman is senior adviser at Washington's Atlantic Council, the prime author of "shock and awe" and author of "The Fifth Horseman and the New MAD: How Massive Attacks of Disruption Became the Looming Existential Danger to a Divided Nation and the World at Large." Follow him @harlankullman.

The views and opinions expressed in this commentary are solely those of the author.