The U.S. and its NATO allies are urgently grappling with a question that once seemed to have faded along with the Cold War: Will Moscow go nuclear?
The big picture: Russian President Vladimir Putin's nuclear threats are growing more direct as his battlefield position in Ukraine grows more precarious.
Driving the news: Sullivan was responding to an address in which Putin confirmed Russia was extending its nuclear umbrella to four newly annexed territories of Ukraine.
Between the lines: Putin seems to believe that if he can convince the U.S. and its NATO allies that he's willing to use nuclear weapons over Ukraine, they will pressure Kyiv to surrender, says Alexander Gabuev of the Carnegie Endowment.
Yes, but: We're not yet at the top of the "escalation ladder," Gabuev notes.
If Putin does use nuclear weapons, he could seek a "demonstration effect" — perhaps by detonating a nuclear weapon over the Black Sea or in the Arctic — or deploy a smaller-yield "tactical" nuclear weapon on the battlefield, says Andrea Kendall-Taylor of the Center for a New American Security.
What to watch: The battering Russia's military is taking in Ukraine could contribute to further nuclear standoffs, even after the war, Kendall-Taylor says.

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