WASHINGTON (NYTIMES) - At the height of the Russian effort in 2016 to manipulate the US presidential election, the CIA had a secret weapon: A mole with some access to the inner circle of Russia's President Vladimir Putin who was able to inform Washington about how the master tactician was thinking about his next move.
That agent was extracted from Russia in 2017, leaving the United States largely blind, for a while, to Mr Putin's thinking.
Now, after five years of slowly rebuilding access to the highest ranks of the Kremlin, US intelligence agencies face a crucial test: Deciphering whether Mr Putin will use the more than 150,000 troops he has amassed near the Ukrainian border to invade, or merely to give him leverage as he dangles the prospect of a diplomatic settlement.
In interviews with officials from the US and its closest allies, it is clear the US and Britain once again have windows into Mr Putin's thinking.
Some intelligence conclusions are reached through electronic intercepts, others bolstered by his periodic conversations with US President Joe Biden, which officials say have proved helpful in understanding Mr Putin's worldview - and his transactional nature.
Mr Putin's calculus, according to a US official, is likely shifting as he weighs the changing costs of an invasion and he assesses what he could get from negotiations.
Several officials note that Mr Putin has a history of waiting until the last possible moment to make a decision, constantly re-evaluating his options.
Not surprisingly, US officials will not say how they know what Mr Putin is thinking, anxious to preserve their current sources.
Knowing the intention of any autocratic leader is difficult, but Mr Putin, who began his career as a KGB officer, is a particular challenge.
Because he avoids electronic devices, oftentimes bans note-takers, and tells his aides little, there is a limit to how much an intelligence agency can learn about his intentions and thinking.
"We do not understand fundamentally, none of us do, what is inside President Putin's head, and so we cannot make any guess about where all of this is headed," Ms Julianne Smith, the US ambassador to Nato, told reporters on Tuesday (Feb 15).
One senior official who has met with Russian counterparts in an effort to defuse the current crisis said recently that the US delegation came away with the sense that Mr Putin's representatives were taking a hard line because they did not know what their boss wanted to do.
US officials are poring over intelligence - both analytic reports and raw material - trying to answer a critical question: how Putin assesses his likelihood of success.
Both US and British officials say that a key element of their analyses is a shared conclusion that something has changed in Mr Putin's assessment of Russia's relative status in the world.
After spending heavily on his military, he now believes Russia is in the strongest position to coerce Ukraine - and the rest of Europe - since the fall of the Soviet Union. His financial reserves have greatly improved Moscow's ability to withstand sanctions.
"Analysts understand how Putin thinks, his grievances and his anger at the West and the United States," said Mr John Sipher, a former Moscow station chief for the CIA. "Now, does that mean we know what he's going to do and when he's going to do it? No, because to do that you have to get in his head."
The US has clearly developed intelligence on the Russian military's war planning, predicting the buildup of troops weeks before it happened, exposing what officials said were Russian sabotage plots and operations meant to create a pretext for invasion.
But the US has long found itself caught by surprise by Mr Putin, from his decision to annex Crimea to his deployment of forces to Syria.
Interestingly, one source of insight to Mr Putin has been conversations with the Russian president himself.
So, like a hostage negotiator, they are determined to keep him talking.
Not long after Mr William J. Burns, the CIA director, visited Moscow in November to warn against an invasion of Ukraine, Mr Biden's aides came up with a plan of constant engagement, setting up a series of negotiations - in Brussels and Geneva, at many different levels - on the theory that while Russia was talking with the West, airing its grievances and making its demands, it was unlikely to invade.
Mr Paul Kolbe, who oversaw collection of Russian intelligence for the CIA for many years, noted recently that "you keep them talking to try to figure out what they really want, to find another way out".
But Mr Kolbe, now the director of Harvard's intelligence project, added, "it made sense - unless what the gunman really wants is to shoot the hostages."
There are limits to what a government should ask its intelligence to do, said Mr Marc E. Polymeropoulos, a former senior CIA officer who oversaw operations in Europe and Russia. Intelligence agencies can provide warning, which is what they have done in recent months. Anything more can be fraught.
"Intelligence is not necessarily predictive of time and date. The intelligence community has done a pretty damn good job of providing policymakers with excellent situational awareness for them to develop policies if Russia goes one way or the other way," he said. "That's what intelligence does. Asking more of that is going to be very difficult."