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Vladimir Putin’s Strategic Choices on the Issue of Ukraine‘s Nuclear Security: A State-of-the-Art Survey and a Dynamic Issue for Ukraine

Some experts say that Mr. Putin did not drop his nuclear threats at first, but put them on hold. Kevin Ryan, a former US defense attache at the Russian embassy in Moscow, wrote recently about Putin’s strategic choices on Russia Matters, a website that examines Russia’s strategic choices.

At the start of the war in Ukraine, the president of the country was told by the president of the United States that he could not have precision missile systems. The White House feared they could tip Russia into reaching for its tactical nuclear weapons.

So far Mr. Putin has been cautious with his cyber-capabilities: He has used them extensively against targets in Ukraine, American and British officials say, but has been reluctant to attack NATO nations and risk bringing them directly into the conflict. And after China’s leader, Xi Jinping, explicitly warned late last year against threatening the use of nuclear weapons, Mr. Putin has quieted down.

Jake Sullivan, a national security adviser to Biden, said on Saturday that the government is a learning agent when it comes to the topic of escalation. “This conflict has been dynamic. It has unfolded over time.” He said Mr. Biden’s decisions have kept up with the changing needs of Ukraine.

In a briefing to reporters on Saturday, Mr. Sullivan repeated Mr. Biden’s two touchstones: “Support Ukraine and its defense and its sovereignty and territorial integrity” while proceeding “in a way that avoids World War Three.”

The administration and its allies now think that even if there is an end to the fighting, Ukraine will still need a long-term deterrent to deter Russia. The F-16 decision may be the best proof that the administration believes that there will be some level of conflict inUkraine for quite some time.

It all raises the question: Are there any conventional weapons in the American or NATO arsenals that the president would not, eventually, provide to Ukraine?

Over the past 15 months, Ukrainian officials say they have known to ignore the initial reply and keep pressing after Washington says yes again. But White House officials say the shifting positions reflect not indecision, but changing circumstances — and changing assumptions about the risks involved.