American intelligence officers are trained to tackle tough targets.
But there are tough targets, and then there's Russian President Vladimir Putin, who plays his cards so closely that it's hard for his own advisers to divine what he's thinking, says Gregory Treverton, chairman of the National Intelligence Council.
"Putin is so isolated that the chances that he might miscalculate and do something rash are top of my list for things I worry about," says Treverton. "I am fond of distinguishing between puzzles — those things that have an answer, though we may not know it — and mysteries, those things that are iffy and contingent. And so how Putin is going to behave is presumably a mystery, and probably even a mystery to Putin."
Treverton is not alone in this view.
Retired Adm. James Stavridis, commander of NATO forces from 2009 to 2013, says Putin is exceptional in how little he telegraphs.
"He certainly has a cabinet of close advisers," Stavridis says."But at the end of the day, the strategic terrain is not on a map somewhere — it's in between Vladimir Putin's ears."
That makes it hard for the CIA and other spy agencies charged with tracking Russian military and economic assets — and with anticipating what Moscow might do next on the conflict in Syria, tensions in Crimea and a wide range of other matters.
Stavridis, now dean of the Fletcher School of Law and Diplomacy at Tufts University, points to a couple of factors that make Putin such a difficult target.
One is the degree of control he has amassed in his 17 years as either prime minister or president of Russia. You have to look to North Korea, Stavridis says, or to Fidel Castro's long reign in Cuba to find another ruler who wields such absolute power.
The tools of espionage — phone intercepts, satellite imagery and more — can sometimes overcome such disadvantages, but may be of limited use against Putin: He's a trained spy himself.
Vladimir Putin joined the KGB in 1975, and was sent to Dresden in East Germany in order to spy on the West during the Cold War. There he learned both near-flawless German and near-flawless spycraft.
"Russia has always had a very strong counterintelligence capability, and Putin would be well-schooled in this," says John McLaughlin, who served as acting director of the CIA in 2004, during Putin's first stint as president. McLaughlin says the aides in whom Putin might confide are mostly ex-KGB, too. "The inner circle there would be very conscious of how they communicate, conscious of who meets whom. So it's a tough environment for intelligence."
But McLauglin adds that if you can't peer into Putin's mind, you still can analyze the realities he's grappling with, which may inform his actions.
"In the case of Russia, you would look at the effect of sanctions, which have been very heavy on them," McLaughlin says. "The fact that the ruble is now at kind of an all-time low, the fact that they have a serious capital-flight problem."
There's also the fact that Putin has spoken openly about his overarching goal of re-establishing Russia as a major world power. It's up to the CIA and other spy agencies to figure out how he plans next to go about it.