In early 2000, I became the first senior U.S. official to meet with Vladimir Putin in his new capacity as acting president of Russia. We in the Clinton administration did not know much about him at the time — just that he had started his career in the K.G.B. I hoped the meeting would help me take the measure of the man and assess what his sudden elevation might mean for U.S.-Russia relations, which had deteriorated amid the war in Chechnya. Sitting across a small table from him in the Kremlin,…