Despising his own era, he wishes that he’d been born in a different century. He ponders the sad mystery of his mother, whom he never knew because she died shortly after his birth. He endures nervous breakdowns, ulcers and shingles. (The index of the book offers seven references to “Kennan, George Frost, intestinal problems of.”) Whenever Kennan was confronted with a serious problem, as Gaddis notes in his biography, he would suffer some sort of breakdown that would allow him to enter a hospital and be cosseted by sympathetic nurses who perhaps served as the surrogate mother he never met. (This isn’t just psychoanalytical license on Gaddis’s part—Kennan himself often considered the possibility that his longings for the opposite sex had a great deal to do with the big hole in his life where his mother should have been.) He struggles with financial straits and the myriad complications of a fantastically peripatetic life (despite his contempt for modern transportation, particularly the automobile). Flashes of titanic arrogance alternate with spurts of virulent self-loathing. As Kennan himself recognized in that remark about his lack of “phlegm,” his was not a personality entirely suited to the harsh give-and-take of high-level politics. Isaiah Berlin, the British philosopher who did a stint as a diplomat at his country’s Moscow embassy in the 1940s, once said of his friend Kennan: “He doesn’t bend. He breaks.”

YET THESE character traits can’t be seen in isolation from the rest of the package. Kennan’s great virtue as an analyst was his ability to see things from the outside. No one was better at tracing out the logical implications of a particular policy in all their elaborate permutations (even if, in so doing, he often ended up overlooking the grubbier but no less important aspects of everyday politics). And this was not despite but because of his own proudly cultivated sense of alienation, his persistent suspicion that he’d been born into the wrong era, or that, above all, he was really a Russian at heart. In a famous interview with George Urban in Encounter, for example, Kennan praised the Soviet Union for its ability to control pornography and expatiated upon his horror at seeing a recent Danish youth festival that was “swarming with hippies—motorbikes, girlfriends, drugs, pornography, drunkenness, noise—it was all there. I looked at this mob and thought how one company of robust Russian infantry would drive it out of town.” (An early draft of this sentiment can be found here in the diaries.)

The notion of “depressive realism,” which argues that sadder people are often better at judging situations for what they really are, has become quite popular these days. (Just think of books like Nassir Ghaemi’s A First-Rate Madness: Uncovering the Links Between Leadership and Mental Illness and Joshua Wolf Shenk’s Lincoln’s Melancholy.) But Kennan was already writing about it (referring to himself in the third person) in his diary in 1942, describing

the conviction that when in a depression he was nearer to reality, to a certain tragic and melancholy reality, than at other times. It was, in other words, not the depression which was abnormal, but the irrational hopefulness, which prevailed at other times.

I think he’s on to something here (even if I’m a bit reluctant to fetishize the insight). For whatever reasons, Kennan certainly had a remarkable ability to step outside of himself and envision alternate realities. I was particularly moved by a moment in the diaries in 1949 when he contemplates the ruins of Hamburg, a city he had lived in before the war and which was obliterated by several days of Allied firebomb air raids. Kennan, who had a complete command of German, is anguished by the destruction of the noble Hanseatic city. He suddenly feels “an unshakeable conviction that no momentary military advantage . . . could have justified this stupendous, careless destruction of civilian life and of material values, built up laboriously by human hands, over the course of centuries.” And then this:

And it suddenly appeared to me that in these ruins there was an unanswerable symbolism which we in the West could not afford to ignore. If the Western world was really going to make valid the pretense of a higher moral departure point—of greater sympathy and understanding for the human being as God made him, as expressed not only in himself, but in the things he has wrought and has cared about—then it had to learn to fight its wars morally as well as militarily, or not fight them at all; for moral principles were a part of its strength.

This critique of the military and moral rationale of the Allied bombing campaign during the war has, over the past decade or so, come into its own—not least, I’m sure, thanks to the comfortable historical distance that has opened up between us and those who actually planned and implemented the destruction. Yet one wonders how many U.S. government officials during the 1940s would have been able to behold the fruits of the policy with the sort of critical distance that Kennan demonstrates. His black, razor-sharp diagnosis of Stalinism—at a time when pro-Soviet wartime propaganda in the United States presented a diametrically opposed picture of the regime—is of a piece with this innate skepticism and independence of thought. He viewed the mendacious pro-Soviet ambassador to Moscow, Joseph Davies, who hailed the show trials and Stalin, with undisguised contempt and revulsion. As his diaries demonstrate, not everything that he concluded was fruitful or wise or perspicacious—and I have to confess that some of the things I learned about the man from this book did diminish his image in my eyes. But I would still insist that it was precisely Kennan’s ability to ask big questions, and his gift for transforming his insights into powerful prose, that made him so unique. Has today’s Washington become more or less inviting to talents of his stature? I’m not entirely sure, though the Kennan chair has yet to be filled and may well remain empty. What I do know is that we condemn him, and those like him, at our own risk. A dose of grumpiness in the right place can work wonders.

Christian Caryl is a senior fellow at the Legatum Institute in London and a contributing editor at The National Interest and Foreign Policy.