Biden’s Armageddon Moment: When Nuclear Detonation Seemed Possible in Ukraine

President Biden was standing in an Upper East Side townhouse owned by the businessman James Murdoch, the rebellious scion of the media empire, surrounded by liberal New York Democrats who had paid handsomely to come hear optimistic talk about the Biden agenda for the next few years.

It was Oct. 6, 2022, but what they heard instead that evening was a disturbing message that — though Mr. Biden didn’t say so — came straight from highly classified intercepted communications he had recently been briefed about, suggesting that President Vladimir V. Putin’s threats to use a nuclear weapon in Ukraine might be turning into an operational plan.

For the “first time since the Cuban Missile Crisis,” he told the group, as they gathered amid Mr. Murdoch’s art collection, “we have a direct threat of the use of a nuclear weapon if in fact things continue down the path they’ve been going.” The gravity of his tone began to sink in: The president was talking about the prospect of the first wartime use of a nuclear weapon since Hiroshima and Nagasaki.

And not at some vague moment in the future. He meant in the next few weeks.

The intercepts revealed that for the first time since the war in Ukraine had broken out, there were frequent conversations within the Russian military about reaching into the nuclear arsenal. Some were just “various forms of chatter,” one official said. But others involved the units that would be responsible for moving or deploying the weapons. The most alarming of the intercepts revealed that one of the most senior Russian military commanders was explicitly discussing the logistics of detonating a weapon on the battlefield.

Fortunately, Mr. Biden was told in his briefings, there was no evidence of weapons being moved. But soon the C.I.A. was warning that, under a singular scenario in which Ukrainian forces decimated Russian defensive lines and looked as if they might try to retake Crimea — a possibility that seemed imaginable that fall — the likelihood of nuclear use might rise to 50 percent or even higher. That “got everyone’s attention fast,” said an official involved in the discussions.