McCain was referring to Putin's earlier career as a skilled operative in the Soviet Union's intelligence services, stationed in Dresden, East Germany. Despite McCain's quip, however, Putin seems to lack a key spy asset: an opaque poker face.
Others have attempted to read Putin's ever so expressive visage. President George W. Bush's first face-to-face meeting with Putin in 2001 was one much-cited example. After looking into the Russian leader's eyes, Bush declared, he now had "a sense of his [Putin's] soul." After the meeting, Bush said he had found the Russian leader to be "very straightforward and trustworthy."
In contrast, Vice President Joe Biden, during a 2011 Moscow visit, told Putin to his face, "I'm looking into your eyes, and I don't think you have a soul." An unfazed Putin, Biden recalled during a later conversation with the "New Yorker's" Evan Osnos, replied with a smile, "We understand one another."
Reading a person's emotions is crucial to fully understanding them and it is true that people's faces best reflect and communicate their emotions. There are two reasons why.
First, facial expressions are universal - so much so that even a person born blind emotes similarly to everyone else. Facial muscle activity and the emotions they reveal aren't learned; they're hard-wired into the brain.
Second, the face is the only place in the body where muscles attach to the skin, which provides quick, real-time information about how someone is feeling.
Read: Emotions are the key in face recognition
So what does Putin's face reveal about his personality and likely actions as Russia's leader?
The place to start is anger. Putin's most frequent look involves his eyes narrowing in anger, an aggressive-approach emotion that conveys the impulse to strike out against others. That other can be Georgia, Ukraine, Russia's internal dissidents - the list is long.
Beyond an aggressive hitting impulse, anger is an emotion about wanting to control one's own destiny and make what one perceives as progress. The anger grows to the extent that the barriers to progress are perceived as unjust.
Secretary of State John Kerry described Russia's meddling in Crimea and eastern Ukraine as "a 19th-century act in a 21st-century world." But Putin's emoting is decidedly here and now. He frequently brings up Russia's traditional symbol of a bear, for example, in asserting that the West will "always try to put it in chains."
Putin's second most frequent emotion is fear, displayed through raised eyebrows and a mouth pulled wide. Again, this emotion greatly informs how Putin sees the world and how, through the filter of his personality, Russia is likely to act. For Putin, there is a deeply felt sense of a need to escape perceived danger to protect both himself and his country.
Fear can make a person freeze and unable to act. But not when it's in combination with anger. That potent mix suggests survival itself is at stake, which spurs assertiveness despite possible adverse consequences.
Third, Putin can, at times, exhibit smirking contempt - particularly for President Barack Obama and what Putin may view as Obama's legalistic, overly nice view of the world order.
Yet apart from anger and fear, the other most important emotion to bear in mind in understanding Putin's psychological makeup is sadness - a sense of disappointment, regret, of feeling forlorn. With Putin, that feeling shows up in closed or lowered eyes, as well as in the down-turned corners of his mouth.
Read: Scientists find why some people have sad faces
As inexorable, as relentless and inflexible as Putin has proven to be in his interactions with the West, so, too, is Russia's geopolitical isolation. The nation remains forever on Europe's periphery, never fully belonging. There's an essential dourness to Eastern Europe that I fully understood only after visiting Russia, the Baltic States, Poland, the Czech Republic and Slovakia.
Given his fundamental wariness, Putin possesses part of this regional trait. He is ever alert to danger, always on duty.
Throughout Eastern Europe, I also noticed a lack of genuine smiles. There seemed a widely shared basic belief that a happy person is an unaware fool.
A joke my translator told me after I gave a speech in Estonia seemed to epitomise this. A man receives a visit from his fairy godmother, the story goes, and she says he can have whatever he wishes for. The catch is that his biggest enemy will get twice the amount of whatever he wishes for.
So what does the man request? Why, that one of his eyes gets gouged out.
That bleak joke tells a lot as to what the West should actually see in Putin's face and personality. He is a man who expects tribulations and is ready to claw his way through them. Whatever the precarious, even dubious, reward.
That both the Russian and Ukrainian economies may continue to buckle under the weight of extended hostilities pales in comparison to keeping the bear free.
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